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Cowpea Breeding for Resistance to Drought and Heat

A. E. Hall and P. N. Patel*



Summary


Drought resistant cultivars are defined as having the ability to produce

relatively high grain yields under drought. Cowpea strains developed at

the University of California, Riverside, by visual selection for early

flowering and high harvest index have produced grain yields of 1 t/ha

when supplied with only 200 mm of water in both California and Senegal.

Under dry conditions in Senegal, these strains took only 60 days from

germination to final harvest. A field screen for improved rooting has

been developed and is being used to search for parents with desirable

rooting characteristics to transfer this trait into cowpeas with

appropriate agronomic traits. Controlled environment and field studies

in California have shown that the high night temperatures which often

occur in the tropics can cause excessive flower abscission in cowpeas by

inducing male sterility. Cowpea strains with tolerance to high night

temperatures have been discovered by screening for the presence of pod

set in the extremely hot field conditions of Imperial Valley, California

during the summer. Heat tolerance has been bred into cowpeas suitable

for California and West Africa. Field tests have been initiated to

determine whether these strains produce higher grain yields in hot

environments.





*Professor and Specialist, Dept. of Botany and Plant Sciences, University

of California, Riverside 92521. Bean/Cowpea CRSP Senegal-UCR Project.





Hall and Patel 2


Introduction

Drought and high temperatures often occur together in the subtropical

and tropical, semiarid zones where cowpeas are grown. It is likely

that drought and high temperatures have interactive effects on

plants. However, in this analysis they are considered separately

because major emphasis is given to the detrimental effects of high

night temperatures, which should have minimal interactions with

drought. Resistant cultivars are defined as having the ability to

produce relatively high grain yields when subjected to stresses,

such as drought and heat.


Breeding for Resistance to Drought

Drought is defined as the occurrence of a substantial water deficit

in the soil or atmosphere. The first step in breeding for resistance

to drought is to determine the type and frequency of droughts that

occur in the production areas for which improved cultivars are

being developed. Hydrologic budget analyses, considering water

inputs from rainfall, soil water storage as determined by soil

physical characteristics and rooting, and crop water use characteristics

can be used to determine the type and frequency of droughts. Most

mechanisms whereby crops resist drought will be mainly effective

against specific types of drought. For example, short cycle, group

flowering varieties are needed where the average period of water

supply is short but reasonably reliable. In contrast, more

indeterminate longer cycle varieties are needed where the average

period of water supply is longer but less reliable.

Deeper and more extensive root systems may increase resistance

to drought if, in an average year, present cultivars do not exploit




Hall and Patel 3


most of the "available" water in the soil profile. However, to be

most effective, quantitative characters such as the extent of

rooting should be expressed at intermediate levels (Hall, 1981).

The extra water gained by increased rooting must more than compensate

for the additional investment of carbohydrates in roots that is

required (Passioura, 1982). The levels of rooting or earliness

that are optimal will depend upon the environment and genetic

background (as they influence the hydrologic budget and plant

responses to drought), and the extent of useful plasticity in

character expression will influence breadth of adaptation (Hall,

1981).


Developing Shorter-Cycle Cowpea Varieties. Hydrologic budget

analyses based upon 44 years of rainfall data predicted that

varieties of annual crops with cycle lengths of 75 days from sowing

to maturity are needed for the northern, drier part of the semiarid

zone in Senegal (Dancette and Hall, 1979). Average rainfall since

1968 has been substantially less in this zone than in earlier years,

and it is likely that varieties with shorter cycles (ca. 65 days)

may be more effective.

In developing shorter-cycle cowpeas, selecting strains with a

shorter vegetative stage, by selecting for earlier flowering, may

be more effective than selecting for a shorter reproductive stage.

Grain yield of cowpea is much more dependent upon the extent of

leaf area development during the reproductive stage than during the

vegetative stage (Turk and Hall, 1980); consequently, selecting for

earlier flowering should not reduce yield potential as much as

selecting for a shorter reproductive period.




Hall and Patel 4


Transgressive segregrants for earlier flowering were selected

in California from progeny from a cross between two day-neutral

cowpeas which flower at the same time (California Blackeye No. 5

and 3ambey 23 flower within 50 to 60 days from sowing in California

depending upon te=-eratures). The earliest selections flowered

four days earlier than the parents at Riverside, California, but

under higher night temperatures in Senegal the parents and selections

flower at the same time (36 days from sowing). Several of the

selections have been more productive than local cultivars in dry

years in Senegal and Sudan (Table 1) where they have a cycle length

of 60 days (with late season drought) to 70 days (under well-watered

conditions). Short cycle cowpeas have also been developed by IITA.

The IT82E-strains were early in Senegal, and IT82E-18 and -56 gave

good yields under dry conditions in Senegal in 1983 (Cisse et al.

1984). Some of these strains appear to be day neutral (IT82E-13,

-16 and -18) and flowered early under long-day conditions in

California, whereas IT82E-3, -10, -32, -56 and -60 flowered late

under these conditions (unpublished data of I. Dow El Madina,

University of California, Riverside). California summer conditions

appear to provide a useful environment for selecting for earliness

which is expressed over a broad range of environments.


Developing Varieties with Improved Rooting. In tropical semiarid

zones, rainfall can exceed crop water use during part of the rainy

season (Hall and Dancette, 1978), and water is then available deep

in the soil profile which is only fully accessible to varieties

with deep and extensive root systems. Available methods for

evaluating the root systems of plants are laborious and severely




Hall and Patel 5


limit the number of genotypes which can be screened. A new method

has been developed which indirectly evaluates rooting under field

conditions (Robertson et al. 1985). It is based upon the time at

which symptoms appear in leaves as an indication of when roots

reach a herbicide band placed deep in-between rows of plants.

Consistent differences among extreme genotypes have been observed

over three seasons, and earliness of symptom appearance was associated

with greater extraction of moisture deep in the soil (Robertson et

al. 1985). Diverse cowpea strains have been screened and genotypes

have been discovered (e.g. Grant, which is similar to California

Blackeye No. 3, and Bambey 21) which may be useful as parents for

conferring improved rooting (Table 2). We are currently attempting

to combine the improved rooting of Grant and the superior canopy

architecture of 8006. Selection for improved rooting is being

conducted under stored soil moisture in a soil at Riverside which

has a high bulk density (1.5 to 1.8 g/cm3) and offers considerable

resistance to root development. A major part of the semiarid zone

of Senegal has "Dior" soil which offers considerable resistance to

root development. Improved capacity for root growth would be

particularly useful in hard soils where the extent and intensity of

rooting is usually poor, and where the improved root growth results

in substantial improvement -in supplies of water and nutrients.


Selecting for Increased Accumulation of Osmotica. Several scientists

Shave proposed that drought resistance may be increased by selecting

for increased osmotic adjustment (Turner and Jones, 1980). We

observed little osmotic adjustment in the leaves of cowpeas, and

little difference in leaf osmotic potential among 100 contrasting




Hall and Patel 6


cowpea genotypes (Shackel and Hall, 1983). For future work it may

be useful to screen for genotypic differences in osmotic potential

in roots, because accumulation of osmotica in root cells could

result in higher turgor and sufficient additional force to increase

root growth in mechanically resistive soils. For shoot tissue

nocturnal osmotic adjustment, as occurs in sorghum (Shackel et al.

1982), could be adaptive if specific reproductive processes occur

at night which are sensitive to the low turgor which can result

from drought.


Developing Varieties with Improved Efficiency for Using Water and

Partitioning Carbohydrate. Varieties with improved seasonal water-

use-efficiency would produce more biomass in dry environments, if

they also have the same total seasonal water use. Unfortunately,

methods for evaluating water-use-efficiency based upon simultaneous

measurements of photosynthesis and transpiration are laborious, and

severely limit the number of genotypes which can be screened.

Theoretical analyses by Farquhar et al. (1982) demonstrated that

measurements of 6 13C on dried leaf tissue could provide a rapid

and sensitive method for measuring relative, integrated, intrinsic

water-use-efficiency under field conditions. Genotypic differences

in water-use-efficiency have been discovered in wheat using this

technique (personal communication with Dr. G. Farquhar, Australian

National University), and we have begun to screen cowpea genotypes,

under drought, for differences in 6 13C in leaves.

In determinate cereal crops, increases in grain yield through

plant breeding have been strongly associated with increases in

harvest index. It is possible that the productivity of the more




Hall and Patel 7


determinate types of cowpeas could be improved by selection for

increased harvest index. Cowpea strains selected visually for

early production of mature pods had higher proportions of shoot dry

matter in grains and grain yield under stored soil moisture (Hall

and Grantz, 1981). However, high harvest index would not be

appropriate for cowpea varieties intended for the production of

both grain and forage, or for the more indeterminate varieties

needed where rainy seasons are long but unreliable with a high

probability of droughts in the middle of the season. Group flowering,

as is present in Bambey 23, may be used to enhance physiological

determinancy and increase harvest index while retaining greater

morphological plasticity than is present in anatomically determinate

genotypes. Group flowering types will exhibit determinancy only if

a substantial number of the early flowers set pods, and are able to

continue to produce floral nodes and flowers later in the season if

early pod-set is low due to mid-season stresses. In contrast,

anatomical determinancy is fixed providing no opportunity for

regrowth late in the season.


Evaluating the Extent of Drought Resistance in Advanced Lines.

Drought resistance depends upon many interacting plant characteristics,

and progress in breeding should be monitored. Multilocation yield

trials are a necessary part of breeding programs, and trials in dry

sites can provide relative measures of differences in drought

resistance among advanced lines. Systems for providing controlled

levels of available water can be used to evaluate genotypic resistance

to a range of drought intensities in one year at one location. The

line-source sprinkler has been proposed as a technique for evaluating




Hall and Patel 8


resistance over a range of drought intensities (Hall et al. 1977).

Unfortunately, the efficiency of the line-source approach is severely

limited by methodological and statistical problems which constrain

data analysis and separation of genotypic differences, and the

water regimes and droughts imposed are usually not natural. The

method of Fischer and Maurer (1978) has distinct advantages for

evaluating the adaptation of advanced lines to semiarid environments.

With this approach, yields of individual varieties must be determined

under drought (YD) and well-watered (YW) conditions. Data on the

average yield of all varieties under drought (XD) and well-watered

conditions (XW) are used to calculate drought intensity (D).

D 1 XD/XW

Then the drought susceptibility (S) of individual varieties can be

calculated from the following relationship.

YD YW (1 SD)

Varieties with average susceptibility or resistance to drought

would have a value of S of 1.0. Values of S less than 1.0 indicate

less susceptibility and greater resistance to drought with a value

of S 0.0 indicating maximum possible drought resistance (no

effects of drought on yield). In evaluating drought resistance

with this method, it is most effective to impose paired wet and dry

treatments on varietal trials at key field test sites. This can be

achieved in many soil conditions, where horizontal transfer of

water is not substantial, by using surface irrigation for the wet

treatment, e.g., plants could be grown on single-row beds, with

adjacent, paired four-row, wet and dry plots. The center furrow

of the wet plot would be irrigated with sufficient frequency to




Hall and Patel 9


maintain an adequate water supply to the two center rows which

would be harvested to obtain a measure of yield potential (Yw).

All of the other furrows would receive the dry treatment, which

would be natural rainfall or limited irrigation. The two center

rows of the dry plot would be harvested to obtain an estimate of

yield under drought (YD)- Varieties or advanced lines would be

randomized, as paired wet/dry treatments, within a block composed

of a set of beds and furrows, and four to six randomized blocks

could be used. Conventional statistical analyses could be used to

evaluate genotypic differences in YW, YD and S for individual

wet/dry varietal trials, or for several multilocation wet/dry

trials. Genotypic differences in S will be most readily detected

in experiments where the intensity of drought is intermediate (e.g.

D values of 0.5). It is possible that the S values of different

types of cowpea varieties will vary when they are subjected to

droughts of different intensities, or at different stages of plant

growth, but this simply indicates that they are better adapted to

certain types of drought and environmental conditions.


A Case for Varietal Intercrops. In tropical semiarid zones, rainfall

during different years may favor either short cycle, group flowering,

erect varieties or longer cycle more indeterminate varieties.

Early cowpea varieties have the additional advantage of providing

food during the period just before the main cereal harvest when

food is often in short supply. Longer-cycle, more indeterminate

varieties have the additional advantage of providing more forage

than early erect varieties. It may not be possible to develop




Hall and Patel 10


extremely plastic varieties which can produce early harvests of

cowpea grain while still retaining the ability to respond to later

rains producing additional grain and forage. Consequently, stability

of farming systems in tropical, semiarid zones may be improved by

sowing at least two types of cowpea varieties (e.g., early erect

varieties and longer-cycle, more indeterminate, spreading varieties).

There are advantages to sowing the different types of cowpea

varieties as an alternating-row, varietal intercrop, instead of as

sole crops in separate fields or as intercrops with different

species, such as cereals. For example, with the first pulse of

rain the early, erect cowpea variety would produce an early harvest

of grain and then senesce. With subsequent rains, the later

spreading cowpea variety would spread over the adjacent rows occupied

by the senescing early variety and produce additional harvests of

grain and then a forage harvest. A possible disadvantage is that

mechanized weeding may be more difficult with a varietal intercrop

than with sole crops of erect varieties. Varietal intercrops of

cowpeas rotated with cereal crops, such as pearl millet, have

advantages over cowpea/millet intercrops. Rotating contrasting

species makes possible more efficient use of manure or fertilizer

(it should be applied to the most responsive crop, which usually is

the cereal), and can slow-down the buildup of pests and diseases

for which only one of the species acts as a host (e.gri -Sti.ge).


Breeding for Resistance to Heat

Resistance to the stress caused by high temperatures requires that

limiting plant processes are not irreversibly damaged. All plant

processes are irreversibly damaged if high enough temperatures are




Hall and Patel 11


imposed for sufficient time. Consequently, the key questions are:

1) what aspects of high temperatures (considering temperature levels

and durations at different times during the season and day) cause

significant reductions in productivity in different climate zones;

and 2) what plant processes and stages of development are most

sensitive to high temperatures, and are responsible for the reductions

in productivity?

For cowpeas, considering the natural variations in temperature

that occur in the tropics and subtropics (Fig. 1 from Nielsen and

Hall, 1985a), and studies on cowpea response to temperature (Warrag

and Hall, 1984a,b), we have concluded that high night temperatures

can be much more damaging to grain yield of cowpeas than high day

temperatures. Growth chamber and field studies demonstrated that

the high eightt temperatures that commonly occur in the tropics can

cause male sterility (Warrag and Hall, 1984b) and substantially

reduce grain yield of cowpeas by increasing floral abscission and

decreasing the number of pods/m2 (Figs. 2 and 3 from Nielsen and

Hall, 1985b). Male sterility, as induced by high night temperature,

is mainly due to lack of anther dehiscence which results from

incomplete pollen development (Warrag and Hall, 1984b). Experiments

involving the transfer of plants between growth chambers with

moderate and high night temperatures (Figs. 4 and 5 from Warrag and

Hall, 1984b) established that the stage of pollen development most

sensitive to high night temperatures occurs 5 to 7 days before

anthesis. High temperatures can also detrimentally influence other

aspects of floral development in certain cowpea varieties. High

temperatures delay or inhibit the development of floral buds in





Hall and Patel 12


CB5, Bambey 21, PI 218123, TVx 12-01E, and IT81D-1020 (unpublished

data of P. N. Patel and I. Dow El Madina). High night temperatures

can induce seed coat browning in TVu4552 (Nielsen and Hall, 1985b)

and this character is inherited as a single dominant gene. We also

observed seed coat browning in TVx 3236-01G plants growing in

Senegal. High day temperatures can result in seeds with assymetric

cotyledons under growth chamber conditions (Warrag and Hall, 1984a)

and in hot field conditions in California (Mackie, 1946).

In developing a program for breeding heat-resistant cowpeas,

we developed a technique for screening for tolerance to heat at

flowering (Warrag and Hall, 1983). This technique consists of

sowing diverse cowpea strains in fields in Imperial Valley, California

in early June. In an average year, most effective screening can be

done only with genotypes that begin flowering during late July and

early August when temperatures are extremely hot (Fig. 6 from Warrag

and Hall, 1983). In these conditions, a few heat-tolerant strains

had abundant pod set, whereas the majority of strains tested

exhibited little or no pod set (Fig. 6 and Table 3 from Warrag and

.Hall, 1983). Unfortunately, this techniques is not useful for

screening late flowering strains, especially those which are sensitive

to photoperiod, because the day lengths are longer than 14 hours during

July in Imperial Valley.

Our studies indicate that Prima and TVu 4552 have substantial

heat-tolerance, which is conferred, mainly, by the same recessive

gene. Growth chamber studies indicated that TVu 4552 may have

greater heat-tolerance than Prima (Warrag and Hall, 1983), but Prima

appears to be a better parent. TVu 4552 has at least two detrimental




Hall and Patel 13


characters: heat-induced browning of the seed coat, and a tendency

for embryo abortion at the end of the pod where it is attached to

the inflorescence. We have made crosses to attempt to transfer

heat-tolerance from Prima and TVu 4552 to CB5, 7977, 58-57, Bambey

21, Mougne, Ndiambour, and IT82E-18. Segregating F2 progeny are

screened for ability to set pods under high temperatures in Imperial

Valley. Selections are screened again in Imperial Valley at the F3

or F4 level depending upon the types of selection conducted in

intervening generations. In Imperial Valley in the summer, the

temperatures are so high that the expression of many agronomic

characters is distorted, and it is necessary to grow lines in more

normal production environments to apply selection pressure for

characters influencing growth habit, canopy architecture, and seed

quality. The high levels of pod set in Imperial Valley by selections,

compared with heat sensitive parents, indicates that progress is

being made in incorporating heat-tolerance. Preliminary yield

tests of heat-tolerant selections (F5's) are being conducted at

this time in California.

Cowpea strains with tolerance to high night temperatures should

be extremely useful where minimum night temperatures exceed 22C

during early flowering stages, e.g., in tropical regions of West

Africa and parts of India (Fig. 1). We have observed that several

cowpea strains developed by empirical breeding procedures in one of

the hottest cowpea production regions of the world (New Delhi,

India) have some tolerance to high night temperatures. In contrast,

many cowpea strains developed in West Africa have low tolerance to

high night temperatures (Table 3). We have not yet evaluated the




Hall and Patel 14


heat-tolerance of traditional late flowering cowpea varieties from

West Africa. For the future, it is necessary to determine whether

selection for tolerance to high temperatures adversely affects

cowpea performance at lower temperatures, because this would

necessitate the development of different varietal types for tropical

and subtropical zones.










ACKNOWLEDGEMENT

This research was supported by Grant No. MSU/AID/DSAN-XII-G-0261

from the United States Agency for International Development to the

Bean/Cowpea Collaborative Research Support Program.





Hall and Patel 15


REFERENCES

Cisse, N., Thiaw, S., and Sene, A. 1984. Project C.R.S.P. niebe

essals varietaux 1983. Institute Senegalais de Recherches

Agricoles. pp 8.

Dancette, C. and Hall, A. E. 1979. Agroclimatology applied to water

management in the Sudanian and Sahelian zones of Africa. In:

Hall, A. E., G. H. Cannell, and H. W. Lawton (eds.), Agriculture

in Semi-Arid Environments 34: 98-118. Ecological Studies,

Springer-Verlag, Berlin, Heidelberg, New York.

Farquhar, G. D., O'Leary, M. H., and Berry, J. A. 1982. On the

relationship between carbon isotope discrimination and the

intercellular carbon dioxide concentration in leaves. Australian

Journal of Plant Physiology 9: 121-137.

Fischer, R. A., and Maurer, R. 1978. Drought resistance in spring

wheat cultivars. I. Grain yield responses. Australian Journal

of Agricultural Research 29: 897-912.

Hall, A. E. 1981. Adaptation of annual plants to drought in relation

to improvements in cultivars. HortScience 16: 37-38.

Hall, A. E. and Dancette, C. 1978. Analysis of fallow-farming systems

in semi-arid Africa using a model to simulate the hydrologic

budget. Agronomy Journal 70: 816-823.

Hall, A. E., Dancette, C., and Turk, K. J. 1977. Crop adaptation

to semi-arid environments, p. 398-418. Proceeding of the

International Symposium of Rainfed Agriculture, Univ. Calif.,

Riverside, Calif.




Hall and Patel 16


Hall, A. E. and Grantz, D. A. 1981. Drought resistance of cowpea

improved by selecting for early appearance of mature pods.

Crop Science 21: 461-464.

Mackie, W. W. 1946. Blackeye beans in California. California

Experiment Station Bulletin 696, pp 56.

Nielsen, C. L., and Hall, A. E. 1985a. Responses of cowpea (Vigna

unguiculata (L.) Walp.) in the field to high night air temperatures

during flowering. I. Thermal regimes of production regions and

field experimental systems. Field Crops Research (In Press).

Nielsen, C. L., and Hall, A. E. 1985b. Responses of cowpea (Vigna

unguiculata (L.) Walp.) in the field to high night air temperatures

during flowering. II. Plant responses. Field Crops Research

(In Press).

Passioura, J. B. 1982. The role of root system characteristics in

the drought resistance of crop plants. p. 71-82. In: Drought

Resistance in Crops with Emphasis on Rice. International Rice

Research Institute, Los Banos, Philippines.

Robertson, B., Hall, A. E., and Foster, K. W. 1985. A field

technique for screening for genotypic differences in root

growth. Crop Science (submitted).

Shackel, K. A., Foster, K. W., and Hall, A. E. 1982. Genotypic

differences in leaf osmotic potential among grain sorghum

cultivars grown under irrigation and drought. Crop Science

22: 1121-1125.

Shackel, K. A. and Hall, A. E. 1983. Comparison of water relations

and osmotic adjustment in sorghum and cowpea under field conditions.

Australian Journal of Plant Physiology 10: 423-35.




Hall and Patel 17


Turk, K. J. and Hall, A. E. 1980. Drought adaptation of cowpea.

III. Influence of drought on plant growth and relations with

seed yield. Agronomy Journal 72: 428-433.

Turner, N. C., and Jones, M. M. 1980. Turgor maintenance by osmotic

adjustment: A review and evaluation. Pages 87-103 in: Adaptation

of plants to water and high temperature stress, eds. N. C. Turner

and P. J. Kramer. New York: Wiley-Interscience.


Warrag, M. 0. A. and Hall, A. E. 1983. Reproductive responses of

cowpea to heat stress: Genotypic differences in tolerance to

heat at flowering. Crop Science 23: 1088-1092.

Warrag, M. 0. A. and A. E. Hall. 1984a. Reproductive responses of

cowpea (Vigna unguiculata (L.) Walp.) to heat stress. I.

Responses to soil and day air temperatures. Field Crops

Research 8: 3-16.

Warrag, M. O. A. and A. E. Hall. 1984b. Reproductive responses of

cowpea (Vigna unguiculata (L.) Walp.) to heat stress. II.

Responses to night air temperature. Field Crops Research

8: 17-33.





Hall and Patel





Table 1. Comparison of Early and Local Cowpeas


SUDAN
SE-GAL (ISRA) (WSARP)

1932 1983 1983

3ambey Louga Bambey Louga El Obeid


Useful Rainfall (=m) 452 181 315 135 230

Cowpea strains Grain Yields (kg/ha)

CB5 x B23

1-2-1 2324 663 1315 250 468
1-11-1 2290 949 1253 188
1-12-3 2406 1091 1816 206 500
3-4-1 2033 919 1445 290
3-4-13 2418 1026 1422 216 355
CB5 23'4 922 1355 195 625

Local

Bambey 21 2263 699 1303 51
Garnel Kabish 135
Gambaru 169


NS 213 NS


LSD .05


81 170






Table 2. Herbicide screening of cowpea strains for rooting in 1983.

Number of Days
UCR # Cowpea Strain Origin to First Symptoms


55
122
237
248
262
251
244
216
255
243
170
39
72
175
260
250
177
247
261
74
217


40
73
176
52
71
180
182
179
156
239
LSD


Bambey 21
Grant
Cross 1-6E-2
Quarenta dias
Reata
CNCX 27-2E
Pittiuba
TVx 3236
CNCX 105-5E
TKx 9-11D (TK-1)
CB5
PI 293579
Vita 3
58-57
Gamusa
CNCX 24-016E
TVx 1841-0-1-E
Serido
Malu
Vita 5
Vita 7 (KN 1)
7977
PI 302457
Vita 4
TVx 1193-FD
88-63
Vita 1
TVx 1836-015J
4R-0269-1F
TVx 309-1G
8006
TVx 133-16D-2
.05 2.7


Senegal
California
Tanzania
Brazil
Mexico
Brazil
Brazil
IITA
Brazil
Tanzania
California
Texas
IITA
Senegal
Mexico
Brazil
IITA
Brazil
Mexico
IITA
IITA
UCD


IITA
IITA
Niger
IITA
IITA
IITA
IITA
UCD
IITA


52.8 a
53.1 ab
53.6 abc
53.6 abc
53.6 abcd
53.7 abcd
54.0 abcde
54.1 abcde
54.2 abcdef
54.5 abcdefg
54.6 abcdefg
54.6 abcdefg
54.7 abcdefg
55.1 abcdefg
55.1 abcdefg
55.3 abcdefg
55.4 abcdefg
55.5 abcdefg
55.6 abcdefg
55.7 abcdefg
55.9 abcdefg
56.0 bcdefg
56.3 cdefg
56.4 cdefg
56.5 cdefg
56.7 cdefg
56.7 defg
56.9 efg
57.3 fg
57.3 fg
57.4 g
57.6 g





Visual evaluation of heat tolerance at flowering of 58 cowpea genotypes in Imperial Valley, CA, 1981

based upon ability to set pods.


High

Prima

TVu 4552t

PI 204647



Moderate
to high

PI 339593



Moderate

PI 293497

Bambey 23

Magnolia

PI 307558


Country
of origin

Nigeria

Nigeria

Turkey







South Africa





USA

Senegal

USA

USA


Low t Coutry Cuntr


Low to
moderate

PI 292899

PI 293550

PI 339604

Bambey 31

Bambey 25

Bambey 24

TVu 354

TVu 3046

TVX12-OIE

CB7

CB

Early Pinkeye

TVu 161

PI 292892

CPI 30783

CPI 11900

CB5


Country
of origin

Hungary

USA

South Africa

Senegal

Senegal

Senegal

Nigeria

India

Nigeria

USA

USA

USA

USA

South Africa

Burma

Argentina

USA


Low

PI 165486

PI 177579

PI 218123

PI 220210

PI 220850

PI 221731

PI 293522

PI 293570

PI 302457

N 70

Bambey 12

Bambey 13

Bambey 14

Bambey 15

Bambey 21

Bambey 22

Bambey 26


Country
of origin

India

Turkey

Pakistan

Afghanistan

Afghanistan

South Africa

USA

USA

USA

Upper Volta

Senegal

Senegal

Senegal

Senegal

Senegal

Senegal

Senegal


Low

Bambey 27

Bambey 28

Bambey 29

Bambey 30

Bambey 32

Vita 4

Vita 5

TVu 401

TVu 984

TVu 1016-1

C-152

CPI 77123

CPI 77122

PI 170859

CPI 30780

PI 124609


Country
of origin

Senegal

Senegal

Senegal

Senegal

Senegal

Nigeria

Nigeria

USA

Nigeria

USA

India

Soviet Union

Soviet Union

Turkey

Burma

India


t Identification codes are: TVu, TVx and Vita, IITA Nigeria; PI, Plant Introduction No. USA; Bambey, ISRA Senegal;


Table 3.




Hall and Patel


42


- 38



34



30


26



22



18



14


10' 1 I I 1 15
JUNE15 JULY I JULY 15 AUG I AUG15 SEPT I SEPT15 California
JULY I JULY 15 AUG I AUG15 SEPTI SEPT15 OCT I West Africa
MAR APRIL MAY JUNE JULY AUG SEPT India
EARLY PLANTING AND LATE PLANTING FLOWERING PERIOD


Fig. 1. Average daily minimum and maximum air temperature during

flowering at representative locations where cowpea are commer-
cially growc.. Tropical locations: Ibadan, Nigeria; Bambey,
Senegal; and Anand, India. Subtropical locations: Kern County,

'CA, and Riverside, CA.





Hall and Patel 22


(0



b= 1.2



b=0.92


S60- 1b=2.33




< 5

W 50-
0
A-




40-
5 50




1982 1983
o oC85 *C85
D TVu4552 APrimo




0 15 17 19 21 23 25 27 29
MEAN MINIMUM AIR TEMPERATURE (C)






Fig. 2. Flower abscission in contrasting cowpea genotypes at

various levels of minimum night air temperature in field

conditions during flowering.




Hall and Patel 23


16 18 20 22
Tmin (C)


24 26 28


Fig. 3. Pod density of early flowers 9 anthesiss occurred during

the first 6 days of higher temperatures), late flowers A

anthesiss occurred 7 or more days after temperatures were

raised), and all flowers of cowpea cultivar CB5.




S ontrol
I00 ---- ---- f-- 24
I days



0 adays
60- AA A
o i-

S\\ 9 days -
u 40i
a. I
20




0 2 4 6 8 10 12 14 16 1718
DAYS AFTER 'FIRST TRANSFER

Fig. 4. Percentage pod set of plants transferred from a growth

chamber at 33/22*C to a chamber at 33/30C day/night temperature

for periods of 3, 6, and 9 days, and then returned to the

33/22*C chamber.



100 -----


80 -

(n 3 days
6j days
II \ >" \ \
C O days
z
Q 40-
at

20


0 .---- control -- --

0 2 4 6 8 10 12 14 16

DAYS AFTER FIRST TRANSFER

Fig. 5. Percentage pod set of plants transferred from a growth

chamber at 33/30'C to a chamber at 33/22*C day/night temperature

for periods of 3, 6, and 9 days, and then returned to the

33/30C chamber.




. s,


Hall and Patel 25












Control (CB5)-- No pods Negligible pods Few pod!
few pods Many pods Many pod!
PI293497 P 293497 PI293497
50- Prima P P339593 P339593
PI2G4647 Prima
TVu 4552 Bombey 2
Prima TVu 455;
4| Magnolia
45 + PI20464
C.- *










30

0 0 0
00 0 0 0





S0 0 0 a 0 0 0
25- 0





> o o o o
00
o 0

0 0 0 0 0 0
20 I I I I I I I 'I I 1
14 16 18 20 22 24 26 28 30 I 3 5 7 9 II 13 15 17 19
1981 JULY AUGUST











Fig. 6. Observations concerning pod set of cowpea strains in

Imperial Valley, California, Shelter air temperatures, includ-

ing daily maximum (0), daily mini-um (o), and the effective day

and night temperatures, calculated from the mean of the daily

mean, and daily maximum and mini-um, respectively.