Genetic Nature and Role of Environment in Sex Expression and Phenological Characters of Pistillate Lines in Castor (Ricinus communis L.)

Abstract

Sex Expression of pistillate lines and their agronomic traits were studied by evaluating six pistillate lines (DPC-22, IPC-30, IPC-31, DPC-9, SKP-84 and M-574) in different environments in India (Hyderabad, Bengaluru, SK Nagar and Junagadh). Stable pistillate expressions even at later order spikes were observed at all locations without any sex reversions to monoeciousness. Interspersed staminate flowers (ISFs) are produced on pistillate spikes for facilitating pollination and maintenance of pistillate lines. Lesser or preferably no ISFs production in pistillate lines is advantageous to maintain genetic purity of castor hybrid seed. Evaluation of genetically diverse pistillate lines in different environments indicated that the expression of interspersed staminate flowers (ISFs) is governed by different temperature dependent genes. It was found that nitrogen and other environmental factors, except temperature, have no role in ISF or sex expression of pistillate lines. We are also the first to report that genes for expression of ISFs and sex reversion are different and not related, though both of their expression depend on temperature. There was no sex reversion in any order of racemes in all the evaluated pistillate lines even at temperatures > 380C and only number of ISFs varied in the pistillate lines in different locations. This study has also established that genetically stable pistillate lines with least or no ISFs and without any sex reversion even at higher temperatures > 320C can be developed by evaluating and selecting diverse pistillate lines in different environments. GGE biplot analysis indicated that the four environments could discriminate the genotypes for the expression of ISFs. SK Nagar, Junagadh and Hyderabad locations were the best testing centres for discriminating the genotypes for stable pistillateness and ISF expression and thereby development of best and stable pistillate lines can be done in these locations. Whereas Bengaluru could be the ideal location for genetically pure castor hybrid seed production as there was no/least expression of ISFs in all the pistillate lines in the location. Pistillate line, IPC-30 had stable pistillate expression with lowest ISFs (0.37 ISFs) than SKP-84 (0.94 ISFs), followed by DPC-22 (4.92 ISFs) and IPC-31 (5.03 ISFs). DPC-22, IPC-30 and IPC-31 had no ISFs in primary spike and S1 spikes in both Hyderabad and Bengaluru locations. IPC-30 had zero to one ISF up to S4 order of spikes in SK Nagar and Junagadh and was the stable pistillate line across the four test environments. Phonological evaluation indicated that DPC-22 and IPC-31 were relatively early flowering with lower node number to primary spike.