Morphological characteristics of pollen from triploid watermelon and its fate on stigmas in a hybrid crop production system

Erandi C. W. Subasinghe Arachchige,Lisa J. Evans,Ulrika Samnegård,Romina Rader

doi:10.1038/s41598-022-06297-2

Abstract

Hybrid crop production is more reliant on pollinators compared to open-pollinated crops because they require cross-pollination between a male-fertile and a male-sterile line. Little is known about how stigma receipt of pollen from male-sterile genotypes affects reproduction in hybrids. Non-viable and non-compatible pollen cannot fertilise plant ovules, but may still interfere with pollination success. Here we used seedless watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) as a model hybrid plant, to evaluate the morphology, physiology, and movement of pollen from inter-planted genotypes (diploids and triploids). We found that pollen from triploids (‘Exclamation’ and ‘Royal Armada’) and diploids (‘SP-6’, ‘Summer Flavor 800’, and ‘Tiger’) was visually distinguishable. Pollen in triploids had more deformities (42.4–46%), tetrads (43–44%), and abnormal growth of callose plugs in pollen tubes. The amount of pollen in triploids to germinate on stigmas was low (8 ± 3%), and few pollen grains produced pollen tubes (6.5 ± 2%). Still, contrary to previous reports our results suggest that some viable pollen grains are produced by triploid watermelons. However, whilst honey bees can collect and deposit pollen from triploids onto stigmas, its effect on hybrid watermelon reproduction is likely to be minimal due to its low germination rate.

Highlights

Hybrid crop production is more reliant on pollinators compared to open-pollinated crops because they require cross-pollination between a male-fertile and a male-sterile line
This form of production is more reliant on pollinators compared to open-pollinated crops as one of the parental lines in hybrid production is functionally male-sterile and requires insects to move pollen from male-fertile lines[4]
For many crops, the physiology of the pollen grains produced by male-sterile flowers has not been quantified and little is known about how the transfer of this pollen onto receptive stigmas affects pollination outcomes

Summary

Introduction

Hybrid crop production is more reliant on pollinators compared to open-pollinated crops because they require cross-pollination between a male-fertile and a male-sterile line. Hybrid crops are produced by crossing selected parental lines, with the objective of producing offspring that have superior genetic characteristics from both parental lines (i.e. hybrid vigour) and generally produce greater yield quantity and/or quality characteristics[2,3] This form of production is more reliant on pollinators compared to open-pollinated crops as one of the parental lines in hybrid production is functionally male-sterile (i.e. does not produce viable and/or compatible pollen grains) and requires insects to move pollen from male-fertile lines[4]. For many crops, the physiology of the pollen grains produced by male-sterile flowers has not been quantified and little is known about how the transfer of this pollen onto receptive stigmas affects pollination outcomes. Pollen that is not viable or compatible cannot fertilise plant ovules, such pollen may negatively affect pollination success through mechanical clogging and/or inhibition of pollen tube growth of viable pollen[15,16]. There is potential for high numbers of non-viable pollen to be deposited on receptive stigmas, with possible negative effects upon plant reproduction

Methods

Results

Conclusion