Genetic variability and molecular responses of root penetration in cotton

Compacted soils restrict root penetration hindering productivity. In this p aper, genetic variability of cotton (Gossipium spp.) root capacity to penet rate hard soil layers and the patterns of gene expression during penetratio n event were investigated. To mimic hard soil layers, wax-petrolatum mixtur es were used. Genetic variability among 27 cotton genotypes for the root ca pacity to penetrate wax-petrolatum disks of 500-700 g wax/kg of mixture was high indicating that breeding efforts targeted to improve this trait can b e successful. In the root tips of a cotton strain with high root penetratin g ability (G. hirsutum HS 200) which penetrated through wax-petrolatum disk s (P), quantify of four polypeptides with molecular weights 35-66 kDa incre ased compared to those root tips which grew in the absence of mechanical im pedance (NP). Differential display showed significant differences in the se ts of mRNA expressed in P and NP roots. Out of a total of 917 cDNAs scored in the differential display experiment, 118 cDNAs, or 13%, were specific to P roots and hence could be associated with the root penetration event. Fur ther detailed study of gene expression in penetrated roots will pinpoint mo lecular factors involved in root penetration ability in cotton. (C) 2000 El sevier Science Ireland Ltd. All rights reserved.