AGRICULTURAL RESEARCH AND EDUCATION CENTER
Hastings AREC Research Report HAS 1987-2 September 10, 1987
Influence of potato cultivars and harvest dates on incidence of bacterial
wilt and tuber brown rot.
r .'i'aj Science
D. P. Weingartner, Assoc. Plant Pathologist Library
J. R. Shumaker, Assoc. Horticulturist 1 8
T 10 1987
History of bacterial wilt in northeast Florida t orida
During the first 50 years of commercial potato production in NEF bacterial
wilt and tuber brown rot caused by Psuedomonas solanacearum E. F. Smith ranked
as one of the four most severe disease problems affecting the crop. Burger
reported the disease in 75% of NEF fields during 1921. Eddins cited losses
of 1.8-8.9% during 1932-38 (5). Eddins (1) during 1929-35 showed that incidence
and severity of the disease could be reduced by lowering soil pH with sulfur
in the summer and then restoring suitable crop production pH levels in the
fall with addition of lime. He also reported that Green Mountain, Katahdin,
and Sebago were tolerant to the disease. The latter two cultivars proved
to be popular with NEF growers and within five years following the introduction
of Katahdin during 1938 the two cultivars were planted on more than 90% of
the NEF acreage. Sebago eventually supplanted Katahdin and from 1946-1981
remained the predominant potato cultivar in NEF (5).
Incidence of bacterial wilt (BW) declined dramatically with the introduction
of and wide use of Katahdin and Sebago. The disease was observed infrequently
during the mid-late 1940's until the mid 1970's and was during this period
considered of minor importance in NEF (5). In recent years due to the higher
solids content of Atlantic and resulting demand for the cultivar among potato
chip processors, acreages of Atlantic dramatically increased in NEF concomitant
with a decrease in acres planted to Sebago. Atlantic is presently planted
on approximately 60% of the NEF potato acreage. Atlantic lacks the tolerance
of Sebago to bacterial wilt and as a result the disease has again become a
serious problem in NEF (5).
Relative susceptibility of modern potato cultivars to BW was reported by
Jaworski et al (2). Data in their paper, however, was based on tests in which
plants were grown in tomato beds having intentionally induced unusually high
bacterial populations. In addition, all plants were also artificially
inoculated with the pathogen. The purpose of the Jaworski experiments was
to identify highly tolerant cultivars for use in a breeding program rather
than to determine levels of tolerance in commercially acceptable potato
cultivars. Aside from Jaworski's report no recent data exist on relative
tolerance of modern potato U.S. cultivars to bacterial wilt under conditions
of natural inoculum.
When BW is discovered in commercial fields, growers are confronted with
determining the most efficient and economic way of managing the brown rot
which will occur in the crop. Based on limited data in Sebago and Pungo
cultivars (D. P. Weingartner unpublished data) it has been suggested that
incidence of brown rot in the lifted crop can be reduced by delaying harvest
and allowing affected tubers to rot in the field. Detailed experimental
evidence was needed to support this recommendation.
During 1986 high incidence of BW resulting from natural soil borne inoculum
occurred in an experiment having 12 replications of six commercial potato
cultivars. This enabled us to follow development of BW from initial onset
to final incidence and severity in the cultivars Ontario, Sebago, La Chipper,
Atlantic, Superior and Red La Soda. In addition, it was possible to harvest
each cultivar on four separate dates over a three week period to determine
the influence of delaying the harvest date on incidence of tuber brown rot
in each cultivar. This report summarizes data from the study.
Potato cultivars were planted 19 February. Temik 15G (20 Ib/acre in-the-row,
40 in spacing) was applied at planting. Cultivars were planted in 24 feet
x four row wide plots. Each cultivar was replicated twelve times with six
replications being in each of two beds. The first BW was observed 7 April.
Some differences in severity of BW among cultivars were observed by 16 April.
Numbers of wilted plants and severity of wilt was determined 24 April.
Individual wilted plants were rated for percent wilt using the Horsfall Barratt
1-12 scale. Data are presented as the means of the sums of wilt ratings for
Single rows containing all 12 replications of each cultivar were harvested
22 and 29 May, 5 and 11 June. Tubers were washed and graded, and visible
brown rot culled. Following grading, all remaining A size tubers were weighed,
counted and cut to detect internal brown rot symptoms. Data are presented
as the percentage of tubers having brown rot.
Results and Discussion
Our observations of incidence and severity of BW agreed reasonably well with
those of Jaworski et al (2). With the exception of Ontario, cultivars in
our test tended to be less severely affected than in Jaworski's test. The
order of susceptibility from least to most severely affected was: Ontario,
Sebago, La Chipper, Atlantic, Red La Soda, and Superior (Table 1). The level
of tolerance in Ontario was outstanding.
In general, the incidence of brown rot observed in harvested, graded tubers
tended to decrease with later harvest dates. There was, however, a significant
(P=.05) harvest date x cultivar interaction (Table 2). The percent brown
rot in Ontario and Sebago did not vary significantly among the four harvest
dates. There were significant differences in brown rot observed within and
among the other cultivars. Even with delayed harvest, however, incidence
of brown rot in Atlantic and Superior were, respectively 6.5 and 5.1%.
Ontario possesses outstanding tolerance to Race 1 of _P. solanacearum, the
predominant race in Florida (3). Although Ontario produced well in this
experiment, it is not a good chipping potato and is also highly prone to forming
secondary stolons and tubers during hot, dry weather (D. P. Weingartner,
personal observations). It is also a late maturing cultivar. It's potential
for use in NEF is therefore limited.
Based on data from this experiment and others (5), the best management program
for reducing incidence of BW and brown rot in NEF potatoes would include
fumigating with 1,3D or metham sodium, planting Sebago or La Chipper, and
delaying harvest for 50-60 days after the first appearance of BW. It is also
important to avoid root injury during midseason cultivation and fertilizer
application. Efforts should be made to minimize or eliminate vine injury
during spraying or other field operations. Even with the best management
practices, however, some bacterial wilt can occur in fields which are
monocultured to potatoes.
1. Eddins, A. H. 1936. Brown rot of Irish potatoes and its control. Florida
Agr. Exp. Sta. Bull 200. 44 pp.
2. Jaworski, C. R., R. E. Webb, R. W. Goth, and S. C. Phatak. 1980. Relative
resistance of potato cultivars to bacterial wilt. Amer. Potato J.
3. Velupillai, M. and R. E. Stall. 1984. Variation among strains of
Pseudomonas solanacearum from Florida. Proc. Fla. State Hort. Soc.
4. Weingartner, D. P. and J. R. Shumaker. 1984. Bacterial wilt and tuber
brown rot as a potential threat to potato production in northeast Florida.
Proc. Fla. State Hort. Soc. 97:198-200.
5. Weingartner, D. P. and J. R. Shumaker. 1983. Nematicide options for
northeast Florida potato growers. Proc. Florida State Hort. Soc. 96:122-127.
Tablet Percent bacterial wilt, severity bacterial wilt, yield
Size Apotatc tubers, and incidence of tuber brown rot in six
potatocultivars during( 1986.
Percent v Ited Sum wilt Yield Incidence
Cultir plants/plot ratings Size A tuber brown
24 Apr 861/ 24 Apr 862/ tubers3/ rot (%)3/
Ontari 0.4 a 0.6 a 264 a 0.2 a
Sebago 4.8 a 9.9 ab 207 ab 0.6 a
La Chiper 8.S a 19.1 F' 185 ab 3.3 b
Atlantc 18.. b 43.7 Lb 124 b 3.6 c
Red LaSoda 28.9 b 69.0 c 143 b 2.6 ab
Superior 45.1 c 130.4 d 67 c 14.0 d
1/ Values within a column followed by the same letter do not differ
2/ Iniividual wilted plants \were rated using 1- 2 iorsfall B&rratt
Scle. I'aximum wilt rating/plot = 444.
3/ Thter yields and incidence of brown rot avci ge across all four
havest dates. Incidence of brown rot reflected those tubers
which went undetected during ,w,'ashing Lnd grading. Yields
expressed as cwt/acre.
Table 2. Incidence (%) tuber brown rot in six potato cultivars harvested on four
dates in 1986.
Harvest Date Sebago Atlantic Ontario Superior Red La Soda La Chipper Mean
22 May 1.0 ab 11.7 e 0.2 a 23.3 g 5.0 cd 7.0 d 8.0 C
29 May 0.3 ab 10.2 e 0.1 a 16.7 f 1.8 ab 3.2 bc 5.4 B
5 June 0.1 a 6.0 d 0.2 a 10.9 a 2.3 ab 1.7 ab 3.5 AB
11 June 1.1 ab 6.5 d 0.2 a 5.1 cd 1.5 ab 1.3 ab 2.6 A
Variety Mean 0.6 A 8.6 C 0.2 A 14.0 D 2.6 AB 3.3 B
1/ Values within cultivar x harvest date, rows and columns followed by the
same case letter do not vary significantly (P=.05) via Duncan's Multiple
Range Test (DMR). Mean value within harvest date column or variety row
followed by the same upper case letter do not vary significantly via DMR.
Data reflect incidence of tuber brown rot following washing and grading.