Effects of pollen competition on progeny performance in a heterozygous cucurbit.

We used an F1 hybrid of zucchini and its wild progenitor to examine the effects of pollen competition on progeny performance. We experimentally varied the intensity of pollen competition by depositing large or small pollen loads onto stigmas. To separate the effects of pollen competition from maternal effects, we excised the styles of flowers receiving the large pollen loads after only the fastest pollen tubes had entered the ovary. The styles from flowers receiving small pollen loads were excised after both fast- and slow-growing tubes had entered the ovary. Consequently, the mature fruits from the two treatments were similar in seed number and weight. Because our previous studies had revealed that fast- and slow-growing pollen tubes fertilize ovules in different regions (locations) within the ovary (fast into region I and slow into region 3), we examined the vigor of the progeny produced in regions I and 3 from both large and small pollen loads. The results revealed that the progeny from large pollen loads outperform progeny from small pollen loads. We also found that for small pollen loads, the progeny from region I outperform the progeny from region 3, which indicates that the progeny produced by the fastest pollen tubes outperform the progeny produced from the slowest.