胚珠異常導致 ‘水晶拔’番石榴少籽並施用GA3提升其著果率

Abstract

‘水晶拔’番石榴 (Psidium guajava L.)穩定少籽，有發展潛力，但少籽原因仍未知，且著果率低，故本研究探討少籽的原因及提高其著果率之方法。 以 ‘水晶拔’與 ‘珍珠拔’為母本，經由不同授粉方式與授粉來源，調查果實內種子數變化。以 ‘水晶拔’為母本時，種子數與種子密度顯著低於以 ‘珍珠拔’為母本之各處理，然而 ‘水晶拔’花粉能使 ‘珍珠拔’形成大量種子，種子數達300粒以上，顯示 ‘水晶拔’花粉具有足夠的正常花粉。 檢視 ‘水晶拔’花粉母細胞減數分裂，了解染色體數目與結構以確認花粉稔性。 ‘水晶拔’與 ‘珍珠拔’花粉母細胞，在減數分裂中期I染色體皆為11對二價體，然而少部分 ‘水晶拔’花粉母細胞染色體有異常，在減數分裂中期I染色體為11對二價體的細胞占51.2%，疑似三染體的細胞占17.4%，疑似轉座染色體的細胞占4.0%，顯示 ‘水晶拔’至少50%花粉其染色體結構與數目正常，可使 ‘珍珠拔’果實形成大量種子，因此花粉並非導致 ‘水晶拔’少籽之主因。 觀察‘水晶拔’開花當天未授粉胚囊，檢視其型態與結構以了解稔性。 ‘水晶拔’正常胚囊僅占13.7%，顯著較少，將異常胚珠歸納為NCAE (normal central cell and egg apparatus)、ACE (abnormal central cell and egg apparatus)、NES (no embryo sac)與OT (other abnormal type)類型，其中 ‘水晶拔’以NES占50.4 %顯著高於 ‘珍珠拔’，推論 ‘水晶拔’高異常比例的胚珠與胚囊，可能導致其少籽。 施用不同濃度GA3以了解其對於 ‘水晶拔’著果率之影響。2007年於開花當天施用GA3，能減緩落果，在花後42天，著果率以100 ppm處理最佳，達70%以上，然而達採收期時，各處理間著果率無差異。2008年於花前1天、花後14天與28天各施用一次50與100 ppm GA3，皆能顯著提高著果率直到果實成熟，著果率達50%以上。GA3促進 ‘水晶拔’著果及單為結果，雖然延遲約50%果實成熟，造成瘤狀外觀，但顯著增加果實大小與果重，提升單株產量。

‘Shuei Jing’ guava (Psidium guajava L.) is an almost seedless cultivar with great potential in Taiwan, but its fruit set and yields are usually low. I studied the cause of seedlessness and the way to increase fruit set in ‘Shuei Jing’ . Different types of pollination and pollen donors were tried for investigating seed number in ‘Shuei Jing’ and ‘Jen Ju’ guava. When ‘Shuei Jing’ was the pollen acceptor, the seed number was significantly less than that of ‘Jen Ju’. However, ‘Shuei Jing’ served as pollen donor resulted in more than 300 seeds when ‘Jen Ju’ was the pollen acceptor. It indicated that pollens in ‘Shuei Jing’ were sufficiently functional for seed formation. The meiosis of microsporocyte was examined in ‘Shuei Jing’. In metaphase I, pollen mother cells with 11 associated bivalent in ‘Shuei Jing’ were as normal as those in ‘Jen Ju’. However, some of pollen mother cells showed aberrant chromosomes in ‘Shuei Jing’. The percentage of normal association, trisomics, and reciprocal translocation were 51.2, 17.4, and 4.0 respectively in ‘Shuei Jing’. There were at least 50% of pollens with normal number and structure of chromosomes in ‘Shuei Jing’. Furthermore, pollination with ‘Shuei Jing’ pollens resulted in numerous seeds in ‘Jen Ju’. These results suggested that pollens were not the main cause of seedlessness in ‘Shuei Jing’ guava. The morphology and structure of embryo sac in ‘Shuei Jing’ were investigated. There were 13.7% of ‘Shuei Jing’ with normal embryo sacs and were significantly less than those of ‘Jen Ju’. The abnormal ovules were classified in four types. NCAE meant the embryo sac with normal central cells but abnormal egg apparatus. ACE meant both central cells and egg apparatus were abnormal in the embryo sac. NES meant no embryo sac within an ovule. OT meant other few abnormal types of ovules. There were 50.4% ovules of ‘Shuei Jing’ belonged to NES and were significantly higher than those of ‘Jen Ju’. These results suggested that high percentage of abnormal ovules might be responsible for seedlessness in ‘Shuei Jing’. GA3 was applied to the flowers of ‘Shuei Jing’ guava to increase the fruit set. GA3 applied on the day of flowering increased the fruit set in 2007. The percentage of fruit set reached 70% in the treatment by GA3 at concentration of 100 ppm on 42 days after flowering (DAF). However, the percentages of fruit set among all treatments were not significantly different when fruits reach maturation. Applied on the day prior to flowering, 14 and 28 DAF with GA3 at 50 ppm and 100 ppm in 2008, the percentage of parthenocarpic fruit and fruit set reached 51% and 63% respectively and significantly higher than that of control. Even GA3 treatment resulted in tumorous appearance and delayed fruit maturation it still enhanced the fruit number, size, and yield in ‘Shuei Jing’ guava.