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Title: Pollen tube growth after intergeneric pollinations of iap-homozygous Sorghum

item BARTEK, M - Texas A&M University
item HODNETT, G - Texas A&M University
item Burson, Byron
item STELLY, D - Texas A&M University
item ROONEY, W - Texas A&M University

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2012
Publication Date: 6/18/2012
Citation: Bartek, M.S., Hodnett, G.L., Burson, B.L., Stelly, D.M., Rooney, W.L. 2012. Pollen tube growth after intergeneric pollinations of iap-homozygous Sorghum. Crop Science. 52:1553-1560.

Interpretive Summary: Frequently there are important traits such as disease and insect resistance that do not exist within an important crop plant but the genes that control these traits do occur in distantly related plants. Unfortunately the plants that have these traits cannot be crossed with the crop plant to transfer the genes that control the desirable traits because they are too distantly related. Recently, researchers discovered a gene in grain sorghum that often allows distantly related plants to cross. It has been determined that this recessive gene in the homozygous condition (iap/iap) allows grassy sorghum plants and sugarcane to successfully cross with grain sorghum. In this study, we wanted to determine if more distantly related grasses would cross with grain sorghum with this gene. A number of different grasses that are distantly related to sorghum were crossed with sorghum and then pollen germination and pollen tube growth through the sorghum female reproductive structure (pistil) was observed with a microscope. Pollen from all the grasses germinated on the sorghum pistil and the tubes grew to different locations within the pistil depending on the species. Based on pollen tube growth, it appears that pollen of corn and buffelgrass has the potential to hybridize with sorghum possessing the iap/iap gene. This research shows that this gene may make it possible to improve grain sorghum by crossing it with very distantly related grass species.

Technical Abstract: Hybridization within Sorghum bicolor (L.) Moench has been the primary means of creating genetic diversity for improvement. While considerable variation exists within S. bicolor, there are traits that could be improved if secondary and tertiary germplasm pools were accessible through hybridization. Sorghum germplasm that possesses the iap allele makes interspecific and intergeneric hybridization more feasible. The objective of this study was to assess the potential of the iap mutant to facilitate intergeneric hybridization across a range of different genera within the Poaceae. Pollen from several species belonging to the genera Miscanthus Andersson, Pennisetum L. Rich., Sorghastrum Nash, and Zea L. was dusted onto the stigmas of S. bicolor lines Tx3361 (with iap allele) and ATx623 (without iap allele). Approximately 24 h after pollination, pollen germination and tube growth in the pistils were observed using fluorescence microscopy. All genera had pollen tube growth and had differential germination and growth among accessions. These findings indicate specific species and individual accessions within species are more important than genera. Significantly more pollen germinated and grew into the pistils of Tx3361 than ATx623 demonstrating the importance of the iap allele; however, lack of pollen adhesion on the stigmas of ATx623 reduced the number of pollen grains available for analyses. These findings indicate that wide hybridization may be possible using Tx3361 as the maternal parent but success may actually depend upon the species and the individual accession used as pollinators. Lack of pollen adhesion may be a legitimate barrier to intergeneric hybridization in S. bicolor but pollen adhesion appears to increase in the presence of the iap allele.