Late Male Fertility in a Glabrous, Male-Sterile (gms) Watermelon Line

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Cucurbit Genetics Cooperative Report 14:85-89 (article 31) 1991

B. B. Rhodes
Department of Horticulture, Clemson University, Clemson, SC 29634-0375

The glabrous character can be fixed in lines heterozygous for gms (2, 3). Although Whitaker and Bemis (4) noted the possibility of using late male fertility for maintaining the gms line, no further study of this phenomenon has been reported. This study was begun when late male-fertility was observed in a putative tetrasomic line segregating for gms that had been cloned in tissue culture from nodal cuttings. This line had previously behaved as a tetrasomic (1).

A sib-pollinated fruit, whjich received pollen from a hairy, male-fertile sibling, produced 155 seed. Selfs and sibcrosses of glabrous, male-sterile x hairy, male-fertile plants were made from the original sibcross. Lines exhibiting male fertility were designated GMF (glabrous male fertile) and lines segregating only for glabrous, male sterile plants were designated GMS. Germination data were recorded as an index of seed viability in the first two generations.

The F1 seedlings from the first fruit segregated 1:1 hairy:glabrous (Table 1). Previous crosses had indicated that the genotypes in the parent lines were gms gms gms gms and + gms gms gms and the F1 genotypes were expected to be the same. Hairy plants from the F1 population were selfed and glabrous plants from this population were sibbed to produce the F2 populations. The hairy plants (+ gms gms gms), when selfed, were expected to produce popuations segregating 3:1 hairy:glabrous, but a ratio of 8:1 was obtained. Germination rates of 70 and 74% were less than the above-90% germinations obtained before with seed from the line. Similarly, two out of 5 F2 populations from sib crosses fit a 2:1 ratio instead of the expected 1:1 hairy:glabrous ratio, and germination rates were less than normal in 4 out of 5 of these F2 populations. Ratios of 8:1 from the selfed hairy F1 plants and 2:1 for the sibbed F1 plants are genetic ratios consistent with that of trisomics if only n+1 gametes are functional. The reduced germination percentages are also consistent with aneuploidy. The original tetrasomic may have lost the extra pair of chromosomes in tissue culture.

The small F3 populations (Table 1) were from selfs of hairy plants, one from a sibbed F2 and one from a selfed F2 plant. The F4 populations were from selfs and sibs of F3 plants. Late male fertility was observed again in the F2 and F5 populations grown at the same time in the greenhouse. GMF.1 was the glabrous, male-fertile line which arose from the F3 seed obtained from selfing a glabrous F2 plant from the sibcross (19 x 18); GMF.2 from the F3 seed obtained from selfing a glabrous F2 plan form the sibcross (25 x 28). GMF.3 and GMF.4 were from the F4 seed obtained from selfing the same F3 plant from the sibcross (4 x 1) twice at a single node. A line segregaring for gms, designated GMS.1, which did not exhibit late male fertility, was maintained by repeating sibbing from an F3 line arising from the original cross. Another glabrous, male-sterile line, designated GMS.2, was not a descendant line of the original late male-fertile plant. GMS.2 was maintained by sibbing and used in crosses with the late male-fertile lines.

Descriptionsof the original four GMF fruit and the two GMS fruit are summarized in Table 2. All progeny of the GMS selfs were glabrous, but only a portion of GMF.2, 3 and 4 were male fertile. Pollen fertility paralled seed set in the three populations observed (Table 3).

Functional male flowers on the GMF lines were three weeks later than male flowers on the hairy plants from the GMS lines (Table 2).

Sterile, non-glabrous plants were not found, as expected if recombination had occurred between two closely linked genes. Rather, a more apt description of late male fertility appears to be a partial restoration of fertility in some glabrous plants. Glabrous male fertile plants, when selfed, produced all glabrous progeny, more of them male sterile than male fertile. Glabrousness behaves strictly as a recessive character, but male sterility does not..

Table 1. Segregating populations of hairy and glabrous watermelon plants from an original cross between a glabrous, male-fertile plant x a hairy, male-sterile tetrasomic plant and the origins of four glabrous male-fertile and one glabrous, male-sterile line.

ID

% Germination

Hairy:Glabrous

Ratio

X2

p
F1 88 19:23 1:1 0.214 0.50-0.70
Hairy F1 selfed (F2);
1 70 54:6 8:1 0.0009 .0.95
18 74 32:5 8:1 0.041 0.50-0.75
Glabrous x Hairy F1 sibbed: (F2):
19 x 18 100 32:19z 2:1 0.125 0.50-0.75
4 x 1 88 39:22 2:1 0.101 0.75-0.90
21 x 18 46 12:11 1:1 0.044 0.75-0.90
22 x 27 82 20:21 1:1 0.024 0.75-0.90
25 x 28 58 16:13y 1:1 0.138 0.50-0.75
Hairy F2 selfed: (F3):
4 x 1 NR* 12:8 2:1 0.446 0.50-0.70
1 NR 3:1 NR NR NR
Hairy F3 selfed (F4):
4 x 1 NR 21:6x 3:1 0.360 0.50-0.75
4 x 1 NR 15:3 5:1 0 >0.95
4 x 1 NR 4:0 NR NR NR
4 x 1 NR 16:3 5:1 0.150 0.50-0.75
Glabrous x Hairy F3 sibbed: (F4):
12.1 x 13.1 NR 16:14 1:1w 0.124 0.050-0.075
15.3 x 15.1 NR 8:1 1:1 5.444 0.010-0.025
15.4 x 15.1 NR 6:5 1:1 0.090 0.75-0.90

z,y,x One glabrous plant was selfed from each of these glabrous populations to produce four glabrous male-fertile families: GMF.1, GMF.2, GMF.3 and GMF.4, respectively. Separate pollinations on the same plant from c produced GMF.3 and GMF.4.
w Sib-pollinations each generations were made to maintain the glabrous, male-sterile line designated GMS.1. A glabrous, male-sterile line unrelated to the late male fertile lines listed above was designated GMS.2 and maiantained by sib-pollinations.
*NR = Not Recorded

Table 2. Comparison of four glabrous male-fertile (GMS) families from self-pollinations of three glabrous plants with two families (GMS) maintained by sib pollinations of glabrous male-sterile x hairy, male-fertile plants.

FAMILYz
GMF.1
GMF.2
GMF.3
GMF.4
GMS.1
GMS.2
Parent Population H:G 36:19 16:13 21:6 21:6 16:14 29:20
selfed: G G G G H H
F1 Population H:G 0:35 0:12 0:33 0:19 35:11 6:2
& Germination 87.5 50.0 89.0 79.0 92.0 NR*
Plants with Male Flowers 0/35 1/11 6/32 5/20 H:all G:none H:all G:none
Days aftery

1st Female

 2 0 1 3 H:5

G:11

 H:2

G:11
1st Malew none 22 21 27 H:5

G:none

 H:2

G:none
Seed/Fruit 23 37 100 68 101 154
S.E. 24 33 55 68 59 107

zGMF is glabrous, male-fertile; GMS is glabrous, male-sterile phenotype. The notation gms refers to the glabrous male-sterile gene. GMS.1 and GMS.2 are lines that segregate 1:1 for hairy (H) male-fertile plantsand glabrous, male-sterile (G) plants. GMF.3 and GMF.4 came from fruit at the same node of the same plant.
yThe first female occured on GMF.2. A day later, a female occurred on GMF.3, etc..
w The first male occurred 21 days after the first female, etc.
*NR = Not Recorded

Table 3. Comparison of seed number in four glabrous, male-fertile (GMF) families and seed number from GMF pollen.

FAMILY
Pollen Source
GMF.1
GMF.2
GMF.3
GMF.4
Seed Number +/- S.E.
SC7 polenz Mean 12 30 93 76
S.E. 2 30 52 71
GMF Pollen: Mean none none 200 178
SC7 fruit S.E 225 90
GMF pollen: Mean 38 90 127 123
sibcross S.E 10 0 101 103
GMF pollen: Mean 29 32 85 63
GMS.1 fruit S.E. 18 26 46 46

zPollen from a diploid line SC7 unrelated to line with glabrous character. Normal seed number of SC7 in the greenhouse is not different from that obtained with GMF pollen.

Literature Cited

  1. Rhodes, B.B. and R.T. Nagata. 1988. Evidence for a tetrasomic ine in watermelon. Cucurbit Genetics Cooperative Report 11:57-59.
  2. Watts, V.M. 1962. A marked male-sterile mutant in watermelon. Proc. Amer Soc Hort Sci 81-498-505.
  3. Watts, V.M. 1967. Development of disease resistance and seed production in watermelon stocks carrying the mgg gene. Proc Amer Soc Hort Sci 91:579-583.
  4. Whitaker T. and W. Bemis. 1976. Cucurbits. pp 64-69. In: Evolution of Crop Plants. Longman, Inc. NY