Inheritance of photo-sensitivity in pigeonpea

Pigeonpea [Cajanus cajan(L.) Millsp.] is a short-day legume species and the late maturing genotypes are more photosensitive than early types. To generate information about the inheritance of photo-sensitivity, this study was conducted under natural and artificially extended (16 h) photo-periods using F_1t F₂ and BC₁F₁ generations. Under natural photo-period, F₁ hybrids showed partial dominance of earliness; while in F₂, a normal distribution that was skewed towards earliness was observed. In contrast under extended photo-period, the spread of F₂ data was wide with discontinuities recorded at day 70, 82 and 103. Chi-square tests, when applied to F₂ and BC₁F₁ data, suggested that three dominant genes (PS₃, PS₂ and PS₃) controlled the expression of photo-sensitivity. These genes were found operating in a hierarchical order with PS₂ and PS₁ genes failing to express in the presence of PS₃ gene. Similarly in the absence of PS₃ gene, PS₂ expressed but it masked the expression of PS₇. Further, PS-i gene expressed only when both PS₃ and PS₂ were in recessive homozygous state. Hence, the proposed genetic model for photosensitivity in pigeonpea is PS₃ > PS₂ > PS₁ and photo-insensitive genotype being a triple recessive ((ps₃ps₃ps₂ps₂ps₁ps₁).