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Copyright 2005, Board of Trustees, University
Ft. Pierce ARC Research Report RL 1979-6 May 1979
EFFECT OF POTASSIUM FERTILIZER RATES ON SEVERITY OF WITE TISSUE
IN FRUITS OF GRAYWALL RESISTANT AND SUS ET oit jARTIE
Norman C. Hayslil I Y j
White tissue, most evident in ripe tomato eA(g/ is lo0ff curs pri-
marily in the outer fleshy walls beneath the cut c stand side
areas of fruits. Brown to black necrotic tissue which may also be present
(Figure 2) is referred to by the author as "graywall". The term, "blotchy
ripening", has been used for both white tissue and brown tissue. Tomatoes with
visible graywall symptoms are thrown out by graders in the packing house. The
severity of white tissue is difficult to determine externally, especially before
tomatoes ripen, and affected fruits are usually not discarded. However, white
tissue lowers the quality and appearance of affected fruits. Resistance to gray-
wall, first detected in Florida breeding lines in 1958 (1), has been incorporated
into all tomato varieties released by the University of Florida since that time,
The severity of graywall on fruits of the Homestead variety was strongly
influenced by the N:K20 ratio in fertility studies on sandy soils at the Agricul-
tural Research Center, Fort Pierce, Florida during the 1960's (2, 4). Based
upon these studies a ratio of 1:2,0-2.5 N to K20 was suggested as a means of
reducing graywall. Growers now use graywall resistant varieties, and many use
a 1:1.5 N to K20 ratio.
Since white tissue was noted to be closely associated with brown tissue
(Figure 2), separate ratings of each were made and reported in 1967 (4). The
amount of white tissue was greatest in low (50 lbs K20/acre) potassium plots in
four separate experiments, as compared to the higher (400 and 800 Ibs, K20/acre)
rates. In one test less white tissue was found in tomatoes from the 800 pound
K20 rate than in the 400 pound rate.
Additional experiments reported here were designed to determine the effect
of potassium rates on white tissue incidence and severity on graywall resistant
and susceptible tomato varieties.
Materials and Methods
Fall. 1967 test. Plots were treated with N-P205-K20 at 200-400-800; 200-400-
400 and 200-400-50 pounds per acre. Sources were: nitrogen ammonium nitrate;
phosphorus 207 super phosphate; potassium 1/2 sulphate of potash and 1/2
muriate of potash. All plots received the same amounts of magnesium and trace
elements. Treatments were made in bands at time of transplanting and bands were
covered with 10-inch-wide plastic strips in an inverted "U" fashion (strip mulch)
(3) to reduce leaching. Tomato varieties, Homestead 24 (graywall susceptible),
and Indian River and STEP 461 (graywall resistant), were seeded in peat pots and
1/ Professor, Vegetable Crops, University of Florida, IFAS, Agricultural Research
Center, Fort Pierce.
transplanted to plots at 24-inch intervals in randomized blocks with four repli-
cations. On December 15 twenty ripe tomatoes were collected at random from each
plot. White tissue and graywall ratings of each tomato were made by inspecting
a thin slice of the fruit shoulder cut perpendicular to the stem scar blossom
scar axis (Figure 3).
Spring, 1968 test. All plots received 200 pounds of N (ammonium nitrate)
and 400 pounds P205 (207 superphosphate) per acre plus magnesium (Emjeo) and
fitted trace elements (FTE 502). Potassium, derived from one half muriate and
one half sulphate of potash, was applied at 50; 200; 400; and 800 pounds of K20
per acre. Other treatments were 200 pounds of K20 per acre as muriate of potash
and the same rate as sulphate of potash. Fertilizer was banded and covered with
Homestead-24 and Indian River varieties were started in peat pots and trans-
planted to replicated plots on January 24. In the field the tomatoes were sub-
jected to cold weather followed by a prolonged dry period. White tissue incidence
was recorded on May 14 on a composite sample of 75 ripe tomatoes taken from the
5 replications of each treatment, using the same method described in the fall,
Fall. 1967 test. Homestead-24 in plots receiving the lowest potassium rate
(50 lbs/K20/acre) had over 5 times as many fruit with graywall as in plots re-
ceiving the highest rate (800 Ibs./K20/acre)(Figure 4) Indian River and STEP
461 had few fruit with graywall at any potassium rate. At 50 Ibs. K20/acre,
Homestead-24 had over 10 times as many fruit with graywall as did Indian River
or STEP 461.
The three tomato varieties had the largest number of fruit with white
tissue and the most severe white tissue at the low potassium rate (Figures 4 and
5). There was a sharp decrease in white tissue severity at the intermediate
rate, and a further reduction in number of fruit with white tissue at the high
rate of potassium.
Spring. 1968 test. Graywall did not develop sufficiently for ratings,
White tissue incidence and severity in this test confirmed the findings in the
tall, 1967 test. White tissue was severe in fruits from the 50 Ibs, K20/acre
potassium rate; much less in fruits from plots receiving 200 Ibs/acre and least
in fruits from plots receiving 400 and 800 Ibs, K20 per acre (Figure 6), There
was little difference in severity of white tissue between graywall resistant
Indian River and graywall susceptible Homestead-24 at each K20 rate, and the
effect of potassium source was negligible.
Graywall resistant Indian River and STEP 461 tomato cultivars appear to
be as susceptible to white tissue development as is graywall susceptible
Homestead-24. The data collected indicate the severity of graywall and white
tissue is affected by or related to the N:K20 rates. The close association
of white tissue and brown tissue in graywall susceptible tomato varieties, and
the similar response of both maladies to N:K20 ratios suggest white tissue and
brown tissue are symptoms of a common problem.
Figure 4. Percent of fruit with white tissue and graywall on three tomato cultivars grown at three levels of potassium
fertilizer. Fall, 1967.
I- WHITE TISSUE
50 400 800
___ L -_ a LI O
50 400 800
LBS. OF K 0 PER ACRE
50 400 800
Figure 5. White tissue severity rating of Homestead-24 tomatoes grown at three levels of potassium fertilizer. Fall, 1967.
LBS. OF KO PER ACRE
Rnn 400 1 50
1 2 3 45 1 2 3 45
I- NONE, 2- SLIGHT, 3- AVERAGE, 4-
1 2 3 4 5
MODERATE, 5- SEVERE
Figure 6. White tissue severity ratings of Indian River and Homestead-24 tomato cultivars grown at four levels of potassium
fertilizer. Spring, 1968.
K0O PER ACRE
3 4 5
2 3 45 2 3 4
I-NONE, 2-SLIGHT, 3-AVERAGE, 4-MODERATE,5-SEVERE
Seven replicated experiments consisting of nitrogen and potassium rates and/
or ratios on field grown tomatoes have been completed. .In every test from which
white tissue and/or graywall ratings were obtained the results were similar: as
potassium rates were increased from low to high at fixed nitrogen and phosphorus
levels, graywall and white tissue severity decreased.
Based on the experiments reported here and those previously reported (1, 2,
4) a fertilizer ratio of 1 N:2 K20 is suggested on South Florida sandy soils for
graywall resistant tomato varieties and 1 N:2.5 K20 for graywall susceptible
tomatoes. It appears that use of ratios of 1:1 or 1:1.5 N:K2P Tay result in
excessive amounts of white tissue and/or browning (graywall) in fruits during
seasons conducive to these problems. The higher rates of potassium should reduce,
but will not always eliminate, these ripening problems.
1. Hayslip, N. C. 1958. Tomato breeding may solve graywall problem.
Sunshine State Agric. Res. Rept. 3(2): 4-5.
2. and J. R. Iley. 1964. Tomato fertility trials on sandy soils.
Proc. Fla. State Hort. Soc. 77:168-172.
3. and J. R. Iley. 1966. Use of plastic strips over fertilizer
bands to reduce leaching. Proc. Fla. State Hort. Soc. 79:132-139.
4. and J. R. Iley. 1967. Influence of potassium on severity
of tomato graywall. Proc. Fla. State Hort. Soc. 80:182-186.