Genetic variation and heterosis for photosynthetic rate in oats

Abstract

Photosynthetic rates were measured for oat (Avena spp.) selections and hybrids using an infrared differential CO?éé analyzer. Rates of photosynthesis were measured at three leaf temperatures (10, 25, and 35 C) and five light levels (.075, .131, .229, .410, and .712 g cal/cm?? .min). The complete set of light treatments was given at each temperature. The dark respiration rate of each genotype also was determined for each temperature. Measurements of CO?éé exchange on all plants were made on the fifth fully expanded leaf of the primary tiller and subsequently on the flag leaf at the time of full panicle emergence. The rate of photosynthesis was measured by sealing a single attached leaf in a leaf chamber and measuring the CO?éé differential between the input and output air streams. The mass uptake of CO?éé was calculated on both leaf area and leaf dry-weight bases. The study involved three separate experiments. The pure-line and hybrid combinations used in Experiment I had shown considerable grain yield heterosis in a previous study. The photosynthetic rates of five Avena sterilis strains and hybrid combinations between A. sterilis and cultivated types were measured in the second experiment. Experiment III consisted of four pure-line oat selections and all possible hybrid combinations among them. These entries were studied to determine whether the maternal parents significantly influenced the photosynthetic rates of reciprocal hybrids. Temperature and light greatly affected the photosynthetic rates of the genotypes tested. Photosynthetic rates increased in a stepwise manner as the irradiance was increased. Light saturation was approached at the highest light level in some genotypes but in many genotypes the slope of the response curves were still quite steep at this light level. Photosynthetic rates were higher at 25 C than at 10 or 35 C for all genotypes tested. Generally, rates were higher at 35 C than at 10 C but there were exceptions, especially at the highest light level. ...