Cucurbit Genetics Cooperative Report 6:64-65 (article 32) 1983
Presence of Factors for Delayed Germination in Citrullus lanatus and Citrullus colocynthis
B. B. Rhodes and Stephen L. Love
Clemson University, Edisto Experiment Station, Blackville, SC 29817
Citrullus lanatus PI 299379 and PI 189225 and Citrullus colocynthis R309 show delayed germination. Since these three genotypes have shown resistance to race 2 anthracnose, we have been particularly interested in germination because poor germination hinders genetic studies.
Shimotsuma (2) studied the hybrid C. lanatus x C. colocynthis and observed that only about 50% of the F1 pollen contained a full complement of chromosomes. Cytogenetic abnormalities in the interspecific hybrid could lead to reduced germination. Lockerman and Putnam (1) reported the presence of inhibitors in the seed coat of cucumber seed. Sowell (personal communication) noted that leaching increases germination in certain Citrullus PIs.
Germination data from families of C. lanatus and C. colocynthis R309 are given in Table 1. Note that less than 1% of the R309 seed and 1.4% of the 299379 seed germinated in an 8 day period, Reciprocal crosses between 299379 and R309 and subsequent progeny showed delayed germination. However, seed from R309 x (R309 x 299379) backcross showed faster germination than either parent.
Distinct differences between R309 and 299379 are evident when these genotypes are crossed with New Hampshire Midget (NHM). Neither R309 nor 299379 showed a reciprocal difference in the F1 generation. However, germination was nil for R309 as a pollen parent in the F1 whereas germination was relatively good for 299379. In fact, in all families surveyed, almost no germination resulted from using R309 as the pollen parent. Additional investigation is necessary to determine whether delayed germination or inviable embryos predominate in this instance.
Recessiveness is indicated in the delayed germination of 299379 since the F1 progeny from crosses with NHM germinated normally and the slowest rate of germination was recorded for the backcross 299379 x (NHM x 299379) and its reciprocal. In the cross with 189225, dominance is indicated by the low numbers of germinating seed in the F1, F2 and progeny from the backcrosses with 299379. Backcrosses with 189225 resulted in substantial germination.
Considerable variability in rate of germination and in actual germination given an unlimited time frame appears to exist in these genotypes. More work will be required to ascertain the genetic basis for these atypical germinating types.
- Lockerman, R. H. and A. R. Putnam. 1981. Growth inhibitors in cucumber plants and seeds. J. Amer. Soc. Hort. Sci. 106(4):418422.
- Shimotsuma, M. 1960. Cytogenetical studies in the genus Citrullus. IV. Intra and interspecific hybrids between C. colocynthis Schrad. and C. vulgaris. Jap. J. Genet. 34(10):303312.