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Identifying Heterotic Blocks on Pearl Millet Chromosomes with Chlorophyll Deficient Mutants¹

Chlorophyll deficient mutant stocks of pearl millet [Pennisetum americanum (L.) Leeke] were crossed with ‘Tift 23’ normal inbred to study the effect of the mutants on the yield of S₁ spaced plants grown in the field. They were also used to identify heterotic blocks on the chromosomes of five pearl millet inbreds that might be used to increase the yield of an F₁ hybrid. Measurements of the 717 S₁ spaced plants from the cross Tift 23 (G/G) x T664 (g/g) showed that when homozygous, the g allele was associated with a golden leaf color and a reduced plant height, plant yield, and seed yield per head of 92, 59, and 64% of the homozygous (G/G) plants, respectively. These heterotic differences (P<0.01) were probably due the interaction of the T664 genes linked to g with the genes on its Tiff 23 counterpart. Thus, the g allele identified and is included in a heterotic block on one segment of one pearl millet chromosome. The remaining blocks would have been equally distributed in the G/g and G/G groups resulting in essentially equal frequencies for all genes except those linked with the g locus. At least 86% (6/7) and probably 93% (13/14) of the genome would have segregated independently. Fourteen recessive chlorophyll deficient mutants (cd is the general symbol for any chlorophyll deficient mutant and Cd is its normal allele) induced in Tift 23 pearl millet were used to identify heterotic blocks in Sx populations of crosses with normal (Cd/Cd) Tift 23 and normal (Cd/Cd) inbreds 13, 18, 104, 166, and 186. The average spaced plant yields of the Cd/Cd and Cd/cd populations from the 14 Tift 23 Cd/cd mutant stocks crossed with the normal Tiff 23 Cd/Cd inbred were 916 and 893 g, respectively, and were not different statistically. Among the 69 S₁ progenies of Tiff 23 Cd/cd x the five normal inbreds Cd/Cd, the heterozygotes were heavier than the homozygotes in 53 cases, 15 of which were significantly heavier (P<0.05 or 0.01). A Tiff 23 mutant stock such as M5 that identified a high yield heterotic block in Inbred 104 (+ 1510**) identified a very low yielding heterotic block (+ 122) in Inbred 186. Thus, it should be possible to increase yields of Tilt 23 x 186 by transferring heterotic block M5 from Inbred 104 to Inbred 186 by backcrossing or by biotechnology at some future date.

Key Words: Pennisetum americanum (L.) Leeke • Heterosis • Near-isogenic population

² Research geneticist, USDA-ARS, and the Univ. of Georgia, College of Agric. Exp. Stn., Coastal Plain Exp. Stn., Agronomy Dep., Tifton, GA 31793.

Received for publication January 21, 1985.