Abstract
Endophytic fungi were once considered detrimental components of cool season pasture grass seed because of their association with toxic compounds. Development of new cultivars of forage grasses infected with nontoxic endophytes suggests endophytes are an essential component of pasture ecosystems. The process of transmitting endophytes via the seed embryo is poorly understood, and little is known about harvest conditions and endophyte transmission or viability. The objective of this project was to develop methods of predicting seed maturity and determine the effect of harvest maturity on viable endophyte transmission to seedling plants. Sixty panicles of tall fescue (Festuca arundinaceae Shreb.) from fields in Georgia and Oregon were sampled from 15 d after flowering until seed freely shattered (Georgia) or seed fields were swathed (Oregon). All fields had previously tested >90% infection with endophyte before the study. Panicles were staged for maturity by scoring for color of the panicle and seed, as well as seed shatter. Chlorophyll was extracted from a fresh subsample of seed, and dry matter was determined from a second subsample. Chlorophyll was estimated by measuring light absorbance at 540 nm. Seed with varying maturity scores were germinated following different prechill conditions. Regression of chlorophyll and dry matter content (dependent variables) with maturity score (independent variable) suggest chlorophyll content (r2 = 0.90) provided a better estimate of maturity than did dry matter (r2 = 0.55). The more mature seed had greater mass, germinated faster, had a higher total germination, and produced more vigorous seedlings. Endophyte transmission into the developing seed was similar within different maturity seed, but infection of seedlings increased from 81 to 91% with seed maturity. We conclude that predicting tall fescue seed maturity by chlorophyll analysis provides a better estimate for seed quality when maintaining endophyte viability is of concern in the harvested seed.
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