THE PERFORMANCE OF LATE BLIGHT GENE Ph-3 IN TOMATO UNDER THE EFFECT OF LOCAL POPULATIONS FROM Phytophthora infestans

Abstract

Since late blight has become a frequent problem in Egypt, it’s important to develop tomato varieties resistant or tolerant to this pathogen. The aim of this research was to assay the performance of late blight resistance gene Ph-3 transferred to some breeding lines and tomato varieties. Five lines (P5, P39, P17, Super marminde and Edkawy) and 3 testers (NC 2 CELBR, NC 25P and 163A) were used in a partial diallel mating desing to generate 15 F1 hybrids. Two individuals greenhouse experiments were conducted for screening the genotypes and evaluation their potencial for faverable traits. The parental varieties and their 15 F1 crosses were screened against late blight under the artificial inoculation with local P. infestans strains. Three disease variables; severity at the end of epidemic (% DS), severity at the half way epidemic (Y50) and the area under the disease progress curve (AUDPC) were used in the screening of resistance. The % DS ranged from 88 % to100 % for the susceptible parental lines while this rate did not exist 21 % for the resistant testes group until the end of the evaluation period. The majority of F1 hybrids exhibited acceptable level of resistance per si, except the crosses resulted from the P05 and P39 with 163A, NC 2 CELBR and NC 25P. Both additive and non-additive gene effects were involved in the inheritance of the resistance to late blight. Mean square values of GCA were larger than SCA for all disease variables where the estimated ratio GCA/SCA were more than 1.00 which indicated that the additive gene effects were more important than the non-additive effects in the inheritance of resistance. Heterosis relative to resistant parent (H2) for % DS ranged from -5.825 % to -37.71 %. Whereas, it was ranged from -43.94 % to -78.95% for AUDPC. Highly and significant heterosis for number of branches, yield and lycopen content were noticed in the hybrid P4 x NC 25P which may be due to sumptuous growth nature of S. habrochaites. The majority of hybrids showed negative heterosis for average fruit weight, while only the hybrid S.marminde x NC 2 CELBR have significant positive heterosis and hybrid vigor. The crosses P39 x NC 25P, P17 x NC 25P and S. marminde x NC25P were the most promising crosses having high frequency of favorable alleles with high genetic variability for selection in the advanced generations.