Pollen-pistil interactions and interspecific-incompatibility among Panicum antidotale, P. coloratum, and P. deustum

Summary

Because previous attempts to produce interspecific hybrids between different Panicum species were unsuccessful, we undertook this study to investigate the impediments to hybridization. Accessions of P. antidotale Retz. (blue panicgrass), P. coloratum L. (kleingrass), and P. deustum Thunb. were self-pollinated and also crossed with one another. Following pollination, pollen germination and tube growth were studied in vivo by observing the pollinated pistils with fluorescence microscopy. Examination of the self-pollinated pistils revealed that pollen germination was approximately 90% for each species and germination occurred shortly after pollination. Pollen tubes grew to the micropyle within one hour after pollination in kleingrass and two hours in blue panicgrass and P. deustum. One P. deustum accession (PI 364953) was self-incompatible with pollen tube inhibition occurring in the style. In the cross-pollinations, the pollen also germinated shortly after pollination, and the overall germination ranged from 77 to 88% for the different crosses. In crosses between kleingrass and P. deustum, most pollen tube growth was arrested shortly after penetration of the stigma papilla, but a limited number of tubes grew to different locations within the stigma. Only four reached the upper part of the style. In crosses between blue panicgrass and P. deustum, the pollen tubes failed to grow beyond the stigma except in one cross where they grew into the upper half of the style. In the blue panicgrass x kleingrass crosses, the tubes grew into the style but were arrested before entering the ovary. In the reciprocal cross the tubes grew into the ovary, but the tubes became disoriented and grew in an apparently random manner, never penetrating the micropyle. Thus, cross-incompatibility systems are responsible for the failure to produce hybrids among these Panicum species.