INFLUENCE OF SPRING DEFOLIATION ON THE POTENTIAL SEED YIELD OF TETRAPLOID HYBRID RYEGRASSES (LOLIUM X BOUCHEANUM KUNTH)

The effect of spring defoliation on the seed yield and seed yield comp onents of three tetraploid hybrid ryegrass varieties differing in head ing date and perenniality was studied in two separate harvest years. O verall, seed yields of Augusta (Italian type) were higher than bAB417 (intermediate type) and bAB424 (perennial type) and increasing perenni ality led to a reduction in mean seed yield. All cutting treatments te nded to reduce seed yields in both years though there were significant interactions with varieties and managements. Augusta, the Italian typ e hybrid was less affected by later cutting than the intermediate type , bAB417 and the perennial type bAB424. The effects of cutting date on forage production and effects on the seed yield and seed yield compon ents of the different hybrids are discussed.