Hebbar K B, Neethu P, Sukumar P Abhin, Sujithra M, Santhosh Arya, Ramesh S V, Niral V, Hareesh G S, Nameer Paingamadathil Ommer, Prasad P V V
ICAR-Central Plantation Crops Research Institute, Kasaragod 671 124, Kerala, India.
Academy of Climate Change Education and Research (ACCER), Kerala Agricultural University, Vellanikkara, Thrissur 680 656, Kerala, India.
Plants (Basel). 2020 Nov 26;9(12):1651. doi: 10.3390/plants9121651.
The reproductive phase of coconut is extremely sensitive to high temperature, manifesting as button (female flower) shedding and poor nut set. The progamic phase, which elapses from pollination to fertilization, is one of the most critical phases during the sexual reproduction processes in annuals and fruit trees and is extremely vulnerable to high temperature. Hence, we investigated the progamic phase of the tall coconut cultivar West Coast Tall (WCT) and the effect of high temperature on the phase under both in vivo and in vitro conditions. Coconut has a long pistil and its length was found to be 18.2 ± 4.9 mm in WCT. Pollen germination on stigma occurred one day after pollination and the pollen tube traversed through the pistil and reached micropyle of ovule four days after pollination at 29 °C. However, high temperature (T > 33 °C), both under in vivo and in vitro conditions, significantly reduced pollen tube growth through the pistil, suggesting its inability to reach the ovule on time to effect fertilization. High temperature also advanced nectar secretion and stigma receptivity and the receptive stigma was dry without nectar, rendering it unappealing to insect pollinators. Thus, both poor pollination and the inability of pollen tube to reach the ovule on time to effect fertilization could be the cause of poor nut set in the coconut variety WCT under high temperature. However, it was encouraging to note that the pollen tube growth was less vulnerable to elevated temperature under high humidity, suggesting that climate change effect on coconut in coastal regions with high humidity might be less severe.
椰子的生殖阶段对高温极为敏感，表现为雌花脱落和坐果率低。从授粉到受精的配子体阶段，是一年生植物和果树有性生殖过程中最关键的阶段之一，极易受到高温影响。因此，我们研究了高种椰子品种西海岸高种（WCT）的配子体阶段以及高温在体内和体外条件下对该阶段的影响。椰子有一个长雌蕊，在WCT中其长度为18.2±4.9毫米。授粉后一天，花粉在柱头上萌发，在29℃下，授粉后四天花粉管穿过雌蕊并到达胚珠的珠孔。然而，在体内和体外条件下，高温（T>33℃）均显著降低了花粉管穿过雌蕊的生长，表明其无法及时到达胚珠进行受精。高温还提前了花蜜分泌和柱头可授性，且有可授性的柱头干燥无花蜜，使其对昆虫传粉者缺乏吸引力。因此，授粉不良和花粉管无法及时到达胚珠进行受精可能是高温下WCT椰子品种坐果率低的原因。然而，值得欣慰的是，在高湿度条件下花粉管生长对温度升高的敏感性较低，这表明气候变化对高湿度沿海地区椰子的影响可能较小。
