The Effect of the Branchless Gene bl on Plant Morphology in Watermelon

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Cucurbit Genetics Cooperative Report 15:74-75 (article 29) 1992

Depei Lin, Tong Wang and Yejun Wang; Xingping Zhang and B.B. Rhodes
Horticulture Department, August 1st Agricultural College, Urumqi, Xinjiang 850003 PR China, Department of Horticulture, E-142 Poole Agricultural Center, Clemson University, Clemson, SC 29634-0375

The branch less variant in watermelon (1) was discovered by Xu Liguan in a watermelon field at Shihezi in Xinjiang Province, PRC, in the late 1960s and named branch less. The verb and adverb aptly describe this variant that branches less than the normal phenotype. Li Shengxion used it as a parent to breed a new variety, ‘Early Branch Less’, a monoecious variety with a dark green fruit. We used this variety to study morphology and genetics of the natural variant. This variant has not previously been reported.

Parents and Progeny. The normally branched breeding line, S173, was the female parent (P1). The male parent (P2) is ‘Early Branch Less’ (EB). Progeny included the F1 (P1x P2), the F2 (F1 selfed), BC1 (F1 x P1) BC2 (F1 x P2). These progeny were generated in Xinjiang Changji Horticultural Farm in 1989-1990.

Field Plots. Seed were planted in the greenhouse at Clemson University on May 5 and transplanted to the field at the Edisto Research and Education Center at Blackville on May 20. Transplants were 5 feet apart on the row and 5 feet apart between rows. Parents and progeny were arranged by order without replication. Fertilizer and spray applications were uniform over the entire field plot area. Number of branches, mains tem length, main stem diameter and leaf length and leaf diameter were recorded on June 19, July 3, and July 9.

Results. The morphology of the branch less phenotype is compared with the normal phenotype in Table 1.

Table 1. The morphology of EB (P2), normal line S173 and F1 (P2 x P1) hybrid plants in field plots at Blackville, SC in 1991.

Main Stem

Leaf

Genotype
Branch no.
Length, m
Diameter, cm
Length, cm
Width, cm
EB (P2) 4.8+ 0.68 2.3 + 0.76 6.7 + 1.11 23.4 + 3.35 20.0 + 3.71
S173 (P1) 10.9 + 3.56 2.5 + 0.50 4.9 + 0.70 19.5 + 2.70 16.0 + 2.04
F1 (P2 x P1) 14.5 + 3.50 3.17 + 0.71 6.4 + 0.88 22.5 + 1.19 18.4 + 1.06

Values are means of 15 plants + standard error. The leaf measured was the 10th on the main stem.

Only half as many branches originated from nodes of the branch less phenotype as the normal phenotype (Table 1), and these branches originated at the first five nodes. No branches originated from the middle and top stems. The F1 mean branch number suggests that the branches from the branch less genotype are different in origin from the branches of the normal genotype. Thus, the total number of branches on the F1 is greater than, rather than less than, on the normal branch.

Segregation for number of branches in parents and progeny is given in Table 2. Chi-Square tests were used to determine the goodness of fit observed to hypothetical segregation ratios in the F2 and BC populations.

Table 2. Branch less segregation in the F2 and reciptocal backcross populations of the cross branch less x normal phenotype in field plots at the Edisto REC, Blackville, SC 1991.

Generation

Observed

Ratio

Chi-Square
total
normal
branchless
normal:branch less
Valuez
df
p
P1(S173) 84 84 0 all normal – – –
P2 (EB) 90 0 90 all branch less – – –
F1(P1 x P2) 84 84 0 all normal – – –
F2 (F1 self) 90 66 24 3:1 0.1037 1 0.75-0.50
BC1(F1 x P1) 62 62 0 all normal – – –
BC2 (F1 x P2) 66 29 37 1:1 0.9848 1 0.50-0.25

z Chi–Square 0.05 = 3.84

The F1 plants were normally branched, the F2 population segregated 3:1 and the BC2 population segregated 1:1 for normal : branch less, respectively, as expected for single recessive gene control of the branch less character (Table 2). We suggest the symbols bl, be used for the gene to describe the character branchless.

Literature Cited

  1. Lin Depei, et al. 1985. Record of melon and watermelon in Xinjiang. Xinjiang People’s Publishing House.
  2. Robinson, R.W., et al. 1976. Genes of the Cucurbitaceae. HortSci 11:554-568.
  3. Cucurbit Genetics Cooperative Gene List Committee. Gene list for watermelon. CGC Report 10:106-110.