Abstract
Spraying with (2-chloroethyl)phosphonic acid (ethephon) to increase femaleness in andromonoecious muskmelon (Cucumis melo L.) increased hybrid seed production under natural field crossing from 12.0% to 27.4% in ‘Wheat City’ and from 4.0% to 51.5% in ‘Queen of Colorado’. A dominant seedling marker (Bi) in ‘Honey Dew’, the pollinator for both crosses, was used to identify hybrid seed.
length (1.9–2.0 cm). Thirty styles were measured from each cultivar to determine the average style length. An additional six reciprocal crosses were designed to determine whether the style length of the female parent could affect seed production. These
1 Professor. 2 Geneticist, DeKalb Seed Co., Argentina. 3 Associate Professor, to whom reprint requests should be addressed. The research work reported in this paper was supported by the Institute of Food and Agricultural Sciences, Univ. of
Abstract
Recommended rates of (2-chloroethyl)phosphonic acid (ethephon) application did not prevent staminate flower formation on summer squash (Cucurbita pepo L.) sufficient to permit hybrid seed production without defloration. The field experiments were conducted in commercial fields in which flower development occurred during warm long day conditions, which promote maleness in squash. A strongly female ‘Cocozelle’ inbred, a strongly male ‘Straightneck’ inbred and a very strongly male ‘Crookneck’ inbred were treated at several seedling stages with rates up to 600 ppm ethephon. Two applications of 400 to 600 ppm ethephon resulted in development of the fewest staminate flowers without significantly reducing seed yield or quality. The ‘Crookneck’ inbred was least responsive to ethephon.
Brassica oleracea is an important vegetable crop, which includes fully cross-fertile cultivars such as broccoli, Brussels sprouts, cabbage, cauliflower, collard, kohlrabi, and kale. F1 hybrids are desirable, as plants grown from hybrid seeds benefit from the heterotic effect of crossing genetically distinct pure lines. But, there is no practical and reliable method to create male sterility for hybrid seed production that is suitable for Brassica vegetables. We have been working to induce nuclear male sterility in cauliflower (Brassica oleracea var. botrytis) by antisense inhibition of Bcp1, a unique anther-specific gene of Brassica. The production of nuclear male-sterile lines will enable male lines with superior agronomic traits to be converted to female parents. Thus, vegetative propagation of parent plants for hybrid seed production by tissue culture is desirable. To achieve this objective, we compared various plant tissues, including stem, petiole, leaf, leaf rib, flower stem, pedicel, flower bud, and petal as explants for tissue culture propagation of an Australian cultivar (B-4) of cauliflower, Brassica oleracea var. botrytis. Four different MS based media containing different amounts of BAP, NAA, GA3, and silver nitrate were used. The cultures were incubated at 25°C with a 16-hr photoperiod. Initial response was visible within 10 days, but percentage callus, root, and shoot formation was scored after 3 weeks of culturing. Of all the explants tested, pedicel explants showed maximum shoot initiation and leaf explant did not respond to regeneration under the conditions tested. The results from these on going experiments will be presented and discussed.
The coupling phase linkages have been synthesized between the gene aw (without anthocyanin) and the male sterile gene ms15 (and its alleles ms26, ms47, and an Israeli source of male sterility). Less than 2 map units separate aw and ms15 on chromosome 2, providing a convenient seedling marker gene to rapidly identify male sterility for both inbred development and hybrid seed production. The seedling marker also provides a convenient marker to rapidly assess hybrid seed purity. Unique features of each of the alleles involved in male sterility and their use in inbred and hybrid development will be described.
Abstract
Suitable parents for the production of F1 hybrid seed between almond and root-knot nematode resistant peach were selected. Three of 13 almond selections were found which, when pollinated by ‘Nemaguard’ pollen, produced good sets of seed. When germinated, their seedlings showed good root-knot nematode resistance, hybrid vigor, and exceptional compatibility with almond tops.
The self-incompatibility of almond was used to permit natural pollination between selection CP5-33 and a selected seedling of ‘Nemaguard’, 3-28. The F1 hybrids proved to be very compatible as rootstocks with almond and peach tops and imparted increased vigor to them.
Both ‘Nemaguard’ and a selected seedlings of ‘Nemaguard’ served as good pollen parents. ‘Okinawa’ peach, another rootknot nematode resistant peach type rootstock, was a less satisfactory pollen parent.
Abstract
High proportions of 3x hybrids were obtained from crosses of 4x highly sexual seed parents by 2x pollen parents in Citrus. This is in contrast to the low proportions usually obtained with 4x partly apomictic cultivars as seed parents, or with 4x plants used as pollen parents. Initial survival of small germinating seeds and very young seedlings was low but later growth vigor has been high. Ten 4x and 9 aneuploid (near 3x) plants were identified.
Abstract
Male-sterile, male-fertile, exserted stigma, and exserted stigma with positional sterile (ps) genotypes of tomato (Lycopersicon esculentum Mill.) were pollinated at daily intervals from one day before to 2 days after anthesis (A-1, A0, A+1, A+2, respectively) in 2 field experiments and one greenhouse experiment. A male-sterile with gene ms-10 35 had greater seeds per pollination than other genotypes in all 3 experiments. Seeds per pollination produced in the greenhouse was greater than that of a similar field experiment at all pollination stages except A-1, where seed production was similar. Seeds per pollination was less at A-1 than at later pollination stages. This was due to significant differences in seeds per fruit in all experiments and percentage of fruit set in 2 of 3 experiments. There was no selfing in the 2 male-sterile genotypes in any experiment and no selfing for exserted stigma with ps in the field experiments. There was about 2% selfing with ps at A+2 in the greenhouse. Selfing with stigma exsertion alone ranged from 2% to 22% in the field and from less than 1% to about 5% in the greenhouse. The relationship of selfing with pollination stage was not clear for the exserted stigma genotype.
Abstract
Broccoli plants homozygous for the ms 6 male sterility gene were grown in the field and greenhouse in several experiments under fluctuating temperatures that averaged from 59° to 64°F. In these environments male sterile plants produced small amounts of pollen with relatively high percentages of abortive grains, and they did not function well in setting seed. In crossing experiments in field and greenhouse, using male sterile seed plants and male fertile pollinators, high percentages of hybrid seed were obtained.