Am J Bot. 1998 Jun;85(6):770.
Self-incompatibility (SI) is an effective method for limiting self-fertilization in flowering plant species, but there are circumstances in which an otherwise functional SI system may fail. One of the most intriguing of these is the induction of selfing by mixed loads of self and heterospecific pollen (the mentor effect) because it is likely to occur under natural conditions, such as in hybrid zones. Here we conducted a series of controlled crosses to determine whether mentor effects operate in two SI annual species, Helianthus annuus and H. petiolaris, and whether the failure of SI results in a decrease in the frequency of hybridization between these two species. Of the 1396 achenes examined from pollen mixtures that included varying ratios of self, intraspecific compatible, and interspecific pollen, 71 (5.1%) were selfed. Selfing frequencies were significantly less than expected based on pollen ratios, except when the proportion of intraspecific compatible pollen was low. Hybridization frequencies from these same pollen ratios averaged 41.8% with H. annuus as the maternal species and 13.3% with H. petiolaris as the mother. Analysis of 1404 achenes from pollen mixtures that excluded self pollen resulted in hybridization frequencies for H. annuus (42.2%) and H. petiolaris (18.2%) that do not differ significantly from those including self pollen. Thus, mentor effects do not appear to play an important role in reproductive isolation between these species. On the other hand, even a modest increase in self-fertilization in hybrid populations, such as that due to mentor effects, could enhance the probability of hybrid species establishment.
自交不亲和性（SI）是限制开花植物物种自交的有效方法，但在某些情况下，原本功能正常的 SI 系统可能会失效。其中最有趣的一种情况是，混合自花和异交花粉负载会诱导自交（导师效应），因为它很可能在自然条件下发生，例如在杂交区。在这里，我们进行了一系列对照杂交实验，以确定导师效应是否在两种 SI 一年生植物 Helianthus annuus 和 H. petiolaris 中起作用，以及 SI 的失效是否会导致这两个物种之间杂交频率的降低。在包括不同比例自花、种内亲和和种间花粉的花粉混合物中，我们检查了 1396 个瘦果，其中 71 个（5.1%）是自交的。自交频率明显低于基于花粉比例的预期值，除了种内亲和花粉比例较低的情况。从这些相同花粉比例的杂交频率平均为 41.8%，以 H. annuus 为母本，H. petiolaris 为母本的杂交频率为 13.3%。对排除自花花粉的花粉混合物中 1404 个瘦果的分析表明，H. annuus（42.2%）和 H. petiolaris（18.2%）的杂交频率与包括自花花粉的频率没有显著差异。因此，导师效应似乎在这些物种之间的生殖隔离中不起重要作用。另一方面，即使在杂种群体中自交频率略有增加，例如由于导师效应，也会增加杂种物种建立的可能性。
