The genetic correlation of panicle shattering with the intact rachilla form of seed retention in Phalaris aquatica L.

Panicle shattering and seed retention are distinct characters that influence seed dispersal in Phalaris aquatica L.(phalaris). One form of seed retention in phalaris is the result of the thickening of the rachilla (intact rachilla) and disruption of the rachilla-break age mechanism. This form of seed retention results in seed dispersal as seed-retaining panicle fragments, providing an opportunity to reduce ant predation of seed, and thereby increase the potential for seedling recruitment. A genetic analysis of panicle shattering and the intact rachilla form of seed retention was conducted on parental clones and derived half-sib families of across between the seed retaining cultivar Atlas PG and the non-seed retaining cultivar Sirocco, grown as spaced plants over two seasons in the field. A simulation of panicle shattering of the parents and families was also devised under glasshouse conditions. The narrow-sense heritability of panicle shattering in the field was 51 ± 10% and 58 ± 12%,on the basis of half-sib family means and parent-offspring regression, respectively,and its genetic correlation with panicle shattering under simulated conditions was24 ± 8%. The narrow-sense heritability of the intact rachilla form of seed retention was 70 ± 17% on a half-sib family mean basis. Seed retention had a negative genetic correlation of 71 ± 19% with panicle shattering, posing a difficulty for breeding seed-retaining cultivars with readily shattering panicles. However, it was considered likely that the two traits were controlled by independent sets of genes and that this association could be broken. This association is discussed in the context of breeding cultivars with seed dispersal characteristics that promote seedling recruitment under conditions of ant predation of the seed bank. This revised version was published online in August 2006 with corrections to the Cover Date.