Effect of Temperature before and after Pollination on Pollen Function in ‘Chanee’ Durian

Hand pollination is commonly practiced in commercial durian orchards to guarantee fruit set and production of evenly shaped fruit. Durian flowers usually contain five locules in the ovary, with each holding 5―7 ovules (Kozai et al., 2014a), which develop into seeds. The seeds are concealed by the edible part of durian, called the aril (Enoch, 1980). The presence of seeds affects durian fruit shape, with fruits having a good shape graded as high quality when traded in the market (Tantrakonnsab and Tantrakoonsab, 2018). Artificial hand pollination is therefore important for production and yield. Pollen function is one of the most important factors determining successful fertilization (Dag et al., 2000; Alcaraz et al., 2011; Matsuda et al., 2011; Kozai et al., 2014b; Pham et al., 2015). Fresh pollen germination has been shown to be optimal at 20―25°C in durian (Kozai et al., 2014b). The same study reported that pollen germination decrease differed between two consecutive years under different temperature regimes, with 15°C having no effect observed compared with 20―25°C in the first year, but a decrease observed in the second year. The difference might have resulted from different temperature conditions during flower opening. The pollen material used in their study was collected at 1900 hours from the orchard, when anther dehiscence had completed. Durian flowers begin to open at around 1600 hours followed by anther dehiscence at approximately 1700 hours, with both ending at around 1900 hours. Growers therefore tend to commence hand pollination using fresh pollen at around 1900 hours; hence collection of pollen at 1900 hours in the experiment by Kozai et al. (2014b). However, the effect of temperature conditions on pollen function during flowering is not yet fully understood. Air temperatures start to decrease at around 1600 hours and can drop below 20°C even during the evening time. Thus, to achieve successful fertilization, it is important to understand the effect of ambient temperatures before and during anther dehiscence (1600 to 1900 hours) on subsequent pollen germination. Pollen tube elongation is also an important factor affecting fruit set and quality (Dag et al., 2000; Matcha et al., 2006; Matsuda et al., 2011; Kozai et al., 2014b; Pham et al., 2015). Kozai et al. (2014b) reported a decrease in pollen tube elongation at both low ( 15°C) and high temperatures ( 30°C) in ‘Monthong’ durian. They further revealed that reproductive development in ‘Monthong’ is also sensitive to low temperatures; however, the information on other cultivars is lacking. Most research on durian is conducted using ‘Monthong’ because it is the dominant cultivar in Thailand. Furthermore, although comparisons of fruit setting (Honsho et al., 2004), ovule development (Kozai et al., 2014a), and pollen germination have been carried out between cultivars (Salakpetch et al., 1992), little is known about how pollen tube elongation is affected by temperature. ‘Chanee’ is another commercial cultivar in Thailand