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Selection for Canopy Temperature Differential in Six Populations of Soybean

Dep. of Agronomy, Mississippi State Univ., Mississippi State, MS 39762
Dep. of Agronomy, Kansas State Univ., Manhattan, KS 66506

^* Corresponding author.

Canopy temperature represents a quantitative measurement of a plant's response to heat and drought stress. Information is needed concerning the genetic variability for canopy temperature (Tc) in segregating populations if plant breeders are to effectively manipulate Tc. This study was conducted to characterize genetic variation for canopy temperature in six populations of soybean [Glycine max (L.) Merr.] and to assess the effectiveness of selection within the populations for canopy temperature. Parent plants, F₁, and F₂ individuals were space planted and a hand-held infrared thermometer was used to monitor plants for Tc on 3 d during late vegetative and early reproductive growth in 1982. Advanced F₃ and F_3:4 lines from each population were monitored in unreplicated progeny rows for Tc following canopy closure in 1983 and the four warmest (HOT) and four coolest (COOL) F_3:4 lines were selected for further study. Selected lines in the F_3:6 generation were replicated in 1984 and monitored for Tc. Heritability estimates for seasonal mean canopy temperature differential (
= canopy temperature — air temperature) based on parent-progeny regression ranged from 1 to 22% for F₂ and F₃ parent-progeny regression; and 0 to 19% for F_3:4 and F_3:6 parent-progeny regression. Rank correlations of F_3:4 vs. F_3:6 lines for
were significant in three of the six populations. The mean
of the HOT vs. COOL selections measured in 1984 were significantly different in three populations, indicating effective F_3:4 selection. Early generation selection for
was not successful in soybean due to low heritability. Manipulation of
in unreplicated F₄ progeny rows was effective in one-half of the populations monitored, however, greater consistency and reliability would have to be achieved before a positive recommendation could be given to use this technology in soybean breeding.

Received for publication February 22, 1988.