The storage life of ‘Clementine’ mandarin (Citrus reticulata Blanco) and Poncirus trifoliata (L.) Raf. pollen was effectively extended in an oxygen-free atmosphere. ‘Clementine’ pollen held at 4°C enabled satisfactory germination (20%) up to 7 weeks; a similar rate of germination was maintained after 20 weeks by use of N atmosphere. By combining deepfreeze temperatures (−18°) with either N or CO2 atmosphere for pollen storage, a germination rate of 13% was maintained after 57 weeks. With Poncirus, lower germination rates were obtained (7-9% after 57 weeks), but results paralleled those obtained with ‘Clementine’ mandarin pollen. Poncirus pollen, stored in an oxygen-free atmosphere at −18° for one year, maintained its fertilizing capacity.
Avocado pollen was germinated in vitro without recourse to germination on the style. The technique employed involved inclusion of pollen grains in liquid medium of 15% sucrose and minerals and application of 1 or 2 drops on 1% agar plus 15% sucrose and minerals. No germination was obtained on agar plus sucrose without placement of pollen in liquid first. Of the cultivars tested, ‘Ettinger’ and ‘Nabal’ pollen germinated best, and ‘Fuerte’ was the poorest. The optimum temperature for germination was 25° to 27°C. Addition of Ca to the liquid proved beneficial.
Normal embryos and seedling plants were obtained from abortive ovules and seeds of seedless grape cultivars ‘Perlette’, ‘Flame Seedless’ and ‘Sultanina’. Plant development was accompanied by callus formation only in ‘Perlette’. The best medium was Nitsch’s with the addition of 10-5m IAA and 10-6m GA3. Excision and culturing of ‘Flame Seedless’ ovules 49 days after anthesis gave higher germination percentages and more viable plants than excision and culturing at anthesis plus 28. Selfed ‘Perlette’ and ‘Perlette’ × ‘Flame Seedless’ ovules cultured at 52 days gave 11%, and the reciprocal cross over 16% well developed seedlings. The significance of the findings for breeding stenospermocarpic grapes is discussed.
In a table grape-breeding program initiated in 1968 at Bet Dagan, the progeny of a cross between the local cultivar ‘Dabouki’ and ‘Cardinal’, has proven of special interest and several selections have been made. One selection is being named ‘Sivan’.
Immature grape embryos from early ripening genotypes of Vitis vinifera were successfully cultured in vitro on Difco orchid agar or a modified White's agar medium. Germination was increased in vitro for five genotypes from 0%, 7%, 11%, 12%, and 16% in vivo to 15%, 24%, 23%, 34%, and 24%, respectively. Subculturing embryos onto liquid culture from seeds that failed to germinate on agar also was possible. Differences in germination rates, as affected by pollen, were significant. This method will allow accelerated development of early ripening cultivars by allowing breeders to use such genotypes as females, as well as males.