Path coefficient analysis and heritability of photosynthetic rate and associated leaf characters in rice varieties

Considerable variation in photosynthetic rates was observed among 32 traditional tall rice varieties while differences were not significant among 16 short statured high yielding varieties (HYV). The maximum rates of even 50–55 mg CO₂dm⁻²hr⁻¹ were recorded in tall rice, Ptb 10, Co 13, Peta and Mahsuri. Leaf photosynthetic rate (Po) was significantly associated with chlorophyll content, leaf nitrogen (N_LA), shorter interveinal distance (IVD) and specific leaf weight (SLW). The relationship with either stomatal frequency or size was loose. Path coefficient analysis revealed that IVD strongly influences Po in traditional tall types. The photosynthetic rates are hertable but with high phenotypic variance. Thus, for rapid field selection shorter IVD may serve as an index for greater photosynthetic efliciency especially in the tall types.