Cucurbit Genetics Cooperative Report 7:64-65 (article 28) 1984

Independence of Genes Ses-B and M in Cucurbita pepo L.

Bloksberg, L.N. and O. Shifriss

Department of Horticulture and Forestry, Cook College, Rutgers- The State University, New Brunswick, NJ 08903

Gene B conditions precocious depletion of chlorophyll in fruits leading to precocious fruit yellowing. In addition, B can deplete chlorophyll in leaves at early stages of plant development leading to leaf yellowing. This effect is particularly severe at low temperatures (3). However, gene Ses-B selectively suppresses the expression of B in leaves (6). Thus, plants of the B/B Ses-B/Ses-B genotype produce precociously yellow fruits, but their leaves appear persistently green as those of B⁺/B⁺ individuals.

Gene M conditions the mottled-leaf characteristic (2). The latter was also described as the silvery-leaf trait (5). This is a complex trait and some data suggest that it can impart a tendency to escape aphid-transmitted viruses (1, 4, 7).

'Jersey Golden Acorn' (JGA) is B/B Ses- B⁺/Ses-B⁺ m/m. It produces precociously pigmented fruits, is susceptible to leaf yellowing, and bears non-silvery leaves. We attempted to substitute Ses-B for Ses- B⁺ and M for m in JGA by crossing it with one of our breeding lines, NJ4, B/B Ses-B/Ses-B M/M, followed by several backcrosses to JGA. This operation gave us an opportunity to study the relationship between Ses-B and M. The data in Table 1 clearly show that the two genes are independent. The incorporation of both Ses-B and M into JGA may increase the economic value of this cultivar.

Table 1. Independence of genes Ses-B and M.
	Number of plantsa in respective classes				Total	Chi square	P
	Ses-B		Ses-B+
	M	m	M	m
P1, 'Jersey Golden Acorn' B/B Ses-B+/Ses-B+ m/m	0	0	1(?)b	29	30	--	--
P2, NJ4 B/B Ses-B/Ses-B M/M	30	0	0	0	30	--	--
F1, P1 x P2	20	0	0	0	20	--	--
BC1, F1 x P1	79	76	76	79	310	0.12	>0.98
F2	89	28	28	12	157	0.63	>0.85
aAll plants were grown under controlled conditions: 16 hr photoperiod, light 11 x 103 lu/m2, 95% from fluorescent tubes and 5% from incandescent bulbs, 20 C day and 15 C night.
bThe origin of this plant is not known, but it could reflect a low penetrance of the silvery-leaf trait among m/m individuals of some background.

Literature Cited

1. Davis, R.F. and O. Shifriss. 1983. Natural virus infection in silvery and non-silvery lines of Cucurbita pepo L. Plant Disease 67:379-380.
2. Scarchuk, J. 1954. Fruit and leaf characters in summer squash. J. Hered. 45:295-297.
3. Shifriss, O. 1981. Origin, expression, and significance of gene B in Cucurbita pepo L. J. Amer. Soc. Hort. Sci. 106:220-231.
4. Shifriss, O. 1981. Do Cucurbita plants with silvery leaves escape virus infection? Origin and characteristics of NJ260. Cucurbit Genetics Coop. Rpt. 4:42-43.
5. Shifriss, O. 1982. On the silvery-leaf trait in Cucurbita pepo L. Cucurbit Genetics Coop. Rpt. 5:48-50.
6. Shifriss, O. 1982. Identification of a selective suppressor gene in Cucurbita pepo L. HortScience 17:637-638.
7. Shifriss, O. 1983. Reflected light spectra from silvery and non-silvery leaves of Cucurbita pepo L. Cucurbit Genetics Coop. Rpt. 6:89-90.