Abstract
Sterility and low seed set in bananas is the main challenge to their conventional genetic improvement. The first step to seed set in a banana breeding program depends on pollination at the right time to ensure effective fertilization. This study aimed at determining bract opening time (BOT) to enhance efficient pollination and seed set in bananas. A Nikon D810 digital camera was set-up to take pictures of growing banana inflorescences at five-minute intervals and time-lapse movies were developed at a speed of 30 frames per second to allow real-time monitoring of BOT. Genotypes studied included wild banana (1), Mchare (2), Matooke (4), Matooke hybrid (1), and plantain (1). Events of bract opening initiated by bract lift for female flowers (P < 0.01) started at 16:32 h and at 18:54 h for male flowers. Start of bract rolling was at 18:51 h among female flowers (P < 0.001) and 20:48 h for male flowers. Bracts ended rolling at 02:33 h and 01:16 h for female and flowers respectively (P < 0.05). Total time of bract opening (from lift to end of rolling) for female flowers was significantly longer than that of male flowers (P < 0.001). On average, the number of bracts subtending female flowers opening increased from one on the first day, to between one and four on the fourth day. The number regressed to one bract on day eight before start of opening of bracts subtending male flowers. There was a longer opening interval between bracts subtending female and male flowers constituting spatial and temporal separation. Bract rolling increased from partial to complete rolling from proximal to the distal end of the inflorescence among female flower. On the other hand, bracts subtending male flowers completely rolled. Differences in BOT of genotypes with the same reference time of assessment may be partly responsible for variable fertility. Hand pollination time between 07:00 and 10:00 h is slightly late thus an early feasible time should be tried.
Highlights
Abbreviations bract opening time (BOT) Bract opening time NARL National Agricultural Research Laboratories IITA International Institute of Tropical Agriculture AA Diploid group of bananas with genome contribution from Musa acuminata AAA Triploid group of bananas with genome contribution from Musa acuminata AAB Triploid group of bananas with genome contribution from Musa acuminata and Musa balbisiana designated as A and B respectively fps frames per second R2 R-squared which is a goodness-of-fit measure for linear regression models
The experiment was conducted at two sites in Uganda; the National Agricultural Research Laboratories (NARL) in Kawanda and the International Institute of Tropical Agriculture (IITA) Sendusu station, Namulonge
Banana bract opening events were generally initiated by bract lifting followed by bract rolling (Table 1)
Summary
Banana (Musa spp.) plants are monoecious where male and female flowers are primarily unisexual and separated on the same inflorescence[1]. They have a year-round flowering habit implying that pollinations can be made all year[2]. Female flowers emerge before male flowers and are usually separated by neutral flowers[3]. This implies that there is no self-pollination within an inflorescence except in some genotypes with hermaphrodite flowers[4]. Flower opening time is a tightly regulated trait in plants, and this determines when and which pollinators are involved in the pollination process. The study found that there is maximum flower visitation frequency at dawn which is believed to be the period of maximum stigma receptivity
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