Theor Appl Genet (1986) 72, 84-87 9 Springer-Verlag 1986 Effect of pollen-style interaction on the pollen tube growth of Gossypium hirsutum* N. J. Gawel and C. D. Robacker Department of Plant and Soil Science, Texas Tech University, Lubbock, TX 79409, USA Received May 9, 1985; Accepted November 11, 1985 Communicated by A. R. Hallauer Summary. All possible crosses among 5 strains of Gossypium hirsutum were made, and the pollen tubes were grown in vivo for 4 h before being fixed, stained and measured. Temperatures ranging from 18.5 to 40.0 ~ were tested for pollen germination and pollen tube growth. The optimal temperature for pollen tube growth was 30.0~ Relative humidity levels of 0 to 100% were used as a pre-pollination treatment of the pollen. Significant differences among the mean pollen tube length of the strains occurred due to pollen x style interactions. The strains also differed in the number of styles which did not support pollen tube growth. These differences were also due to pollen x style interactions. Pollen and style strains could be ranked according to their relative contribution to pollen tube length. Key words: Gamete competition - Pollen tube growth - Pollen germination - Pollen-style interaction Introduction Pollen, the male gametophyte, has been the subject of relatively little genetic research compared to the sporo- phyte. However, studies have been done which demon- strate that pollen can be considered not only as a part of the sexual reproduction process in plants, but as a separate, metabolically active organism with half the genetic complement of the parent plant. Pollen from genetically diverse plants have genetically different vegetative nuclei, and hence discernable differences in pollen tube growth (Barnes and Cleveland 1963; Sari Gorla etal. 1975). The expression of genes at this * College of Agricultural Sciences Publication Number T-4-189 gametophytic level could provide an additional stage (in addition to the sporophytic level) at which geno- types could be selected for research or breeding pro- grams. Genes which are expressed in the sporophytic stage of a plant have been shown to be expressed in the gametophytic stage as well. Ter-Avanesian (1978) suggested a link between pollen tube competition and variability of resulting progeny in Gossypium hirsutum. In Zea mays (Mulcahy 1974) and Dian- thus chinensis (Mulcahy and Mulcahy 1975), seedlings pro- duced from faster growing pollen tubes were more vigorous than those from slower growing tubes. Zamir etal. (1981) demonstrated that pollen produced by cold tolerant Lycopersi- con hirsutum plants was better adapted to functioning at cold ,temperatures than was pollen from L. esculentum, a non-cold tolerant species. In other studies with L. esculentum, Tanksley et al. (198t) found that 60% of the structural genes coding for 9 sporophytic enzyme systems were expressed in the gameto- phyte. To develop methods of screening genotypes for desirable traits at the cellular level, it is important to understand the effects of pollen and style genotype and various environmental factors on pollen tube growth rate. In the present study, the objective was to deter- mine the contribution of both pollen and stylar geno- type on pollen tube growth rate. The effects of different levels of temperature and relative humidity were also examined. Materials and methods Five Gossypium hirsutum strains were chosen on the basis of their relatively different sporophytic characteristics. They were: T25 (non-wilting), T169 (readily-wilting), T141 (slow- growing), T147 (fast-growing), and Texas-Marker-1 (TM1), a long-term inbred strain of'Deltapine 14'. All possible self and cross pollinations were performed in vivo. To determine the optimum temperature for pollen tube growth, the pollinated styles were incubated in petri