Red rot disease resistance in interspecific hybrids of sugarcane derived from diverse cytotypes of Saccharum spontaneum L.

Red rot disease has caused major loss to sugarcane crops for more than a hundred years.  It  is caused by the fungal pathogen Colletotrichum falcatum Went. In sugarcane breeding, the development of resistant varieties through inter varietal hybridization is a major challenge. Pre-breeding is an ideal approach to incorporate resistance. Saccharum spontaneum, the wild species of sugarcane has been utilized in sugarcane breeding since 1912 owing to their wider adaptability to biotic and abiotic stresses. It shows cytomorphological diversity with 41 cytotypes from 2n=40-128.The major cytotypes are 2n=40, 2n=48, 2n=56, 2n=60, 2n=64, 2n=72, 2n=80, 2n=88, 2n=96, 2n=112, 2n=120 and 2n=128, of which the cytotype 2n=64 is the predominant one. The actual frequency and level of red rot resistance in the hybrids derived from different ploidies /cytotypes of S. spontaneum are yet to be ascertained. About 588 hybrids derived from 37 interspecific crosses involving eight commercial varieties and 16 clones of S. spontaneum with eight cytotypes (2n=40, 56, 60, 64, 72, 80, 88, 112) were evaluated for red rot resistance at 6th  month under controlled condition using the pathotype CF 06 (Cf 671). Resistance observed in 44.3% of the hybrids in which 28.9% was MR and 15.4%  of  R  types.  Differential  segregation  of  chromosomes  from  different  cytotypes  imparted  differential  reactions  in  the progenies to red rot pathogen. The progenies with 2n=40, 64, 72, 80, 88 and 112 imparted resistance at higher frequency from 31.5% to 56.0%. The contribution of lower cytotypes for imparting resistance was 43.5% (2n=40), 19.4% (2n=56) and 16.0% (2n=60). Among the lower cytotypes, higher frequency of resistance with 2n=40 is due to the segregation of the whole genomic complement of 40 chromosomes of male gamete (S. spontaneum) to the progenies through n+2n transmission. Though 64 cytotype derived hybrids had 32 chromosomes through n+n transmission they sustained resistance in 48.7% of progenies. Among the higher cytotypes, 88 and 112 produced maximum resistant progenies at a frequency of 56%. It indicates that enhanced ploidies with the higher male genomic/gametic component impart resistance at a higher frequency. It is advantageous for sugarcane breeding to attain stable resistance. Hence, this study suggests utilizing the resistant hybrids of the higher cytotype derived crosses for nobilisation to achieve horizontal/stable resistance.