Pollen biology in relation to artificial hybridization in the genus Protea

[摘要] ENGLISH ABSTRACT: Effects of pH,sucrose, boric acid and temperature on in vitro germination of pollen ofProtea repens (L.) L. cv. 'Embers' were investigated in hanging-drop culture to establishoptimum conditions for germination. Optimum values were found within ranges pH: 5 - 8,sucroseconcentration:0.4 - 0.7 M, boric acid concentration:50 - 500 mg.e-1, and incubationtemperature: 5 - 30°C. Storage temperature and humidity on pollen viability was studiedin four Pro tea clones. Pollen was stored at a range of temperatures and relative humiditiesfor up to one year and tested for ability to germinate in vitro. Pollen of P. repens cv.'Sneyd', P. eximia cv. 'Fiery Duchess' andP. magnifica clone 'T 84 07 OS', stored in liquidnitrogen (-196°C) and in a freezer (-14° to -18°C), retained a germination percentage as highas that of fresh pollen regardless of humidity. The study showed that long-term storage ofprotea pollen is not feasible at temperatures above O°C. The correlations between thefluorochromatic reaction (FCR) and germinability were found to be low and nonsignificant.Fifteen month old cryopreserved 'Sneyd' pollen was shown to retain its ability to fertilize andset seed equal to that of fresh pollen. 'Sneyd', 'Fiery Duchess' and 'T 84 07 OS' pollencould be repeatedly thawed and frozen in liquid nitrogen before its germinability in vitrodecreased. The morphology and size of Protea pollen was studied, using light and scanningelectron microscopy. Polymorphic grains were observed in two interspecific hybrids. Verysmall differences in pollen grain size were recorded between clones/species. The malefertility of 25 interspecific Pro tea hybrids, based on in vitro pollen germinability, wasinvestigated. The majority of hybrids were found to be sufficiently fertile to be used in abreeding programme. Pistil structure and pollen tube pathways were investigated in 'Sneyd'using light and scanning electron microscopy. The pistil had four distinct regions, consistingof the stigma, the vertebra-shaped upper style, the heart-shaped lower style, and the ovary.The pistil had a stylar canal along its entire length and this canal was also the route by whichpollen tubes grew to the ovary. Very low numbers of pollen tubes reached the ovary. Thebreeding system of 'Sneyd' and 'Fiery Duchess' were determined from pollen tube and seedset data, after controlled hand-pollinations. Both clones were found to be fully selfcompatible.Very low percentages autogamous seed set were recorded. Interspecific crosseshad a low success rate. An incompatibility reaction probably occurred on the stigma and/or in the upper style regions.The attainment of maximum stigma receptivity of two Proteacultivars was investigated by means of seed set experiments, pollen tube growth observationsand measurement of the degree of opening and closing of the stigmatic groove. Bothcultivars were found to be protandrous. The maximum stigmatic groove width of bothcultivars never exceeded the pollen grain diameter. It was concluded that Protea spp. mustbe hand-pollinated two to six days after anthesis in order to obtain maximum seed set; whilefor the observations of pollen tubes in the ovary, inflorescences must not be harvested beforeseven days after pollination.

[发布机构] Stellenbosch University