Inheritance To The Blast In Japonica Landraces From Taihu Lake Region And Mapping Of Resistance Genes

Rice(Oryza sativa L.) is one of the important monocotyledonous crops in the world, and provides the staple food for more than half of the world's population.Rice blast, caused by Magnaporthe grisea(Hebert) Barr,is one of the most widespread and destructive diseases of rice.Breeding and utilizing resistant cultivars are the most effective and economical way of controlling blast disease.And the Japonica landraces in Taihu lake area is one of the special genetic resources treasury in China,and this region have a long history of rice cultivation,and possess many diverser type varieties. Rice landraces have broad spectrum and strong resistance to rice blast strains because of rice variety have been co-evolved with rice blast so a long time.The study work of genetic and mapping resistance genes of Japonica landrace varieties in Taihu lake area have really meaning in resistance breeding for Yangtze River area in China.The race classification of twenty-six blast isolates coming from various provinces regions in China were re-identified according to their reaction in seven Chinese blast differentials,and the seven Japanese differential rice blast strains also re-identified according to their reaction in twelve Japanese rice differentials.The results were compared with their previous classifications from Institute of Plant Protection of Jiangsu,Zhejiang,Guangdong,Fujian,Hunan or Sichuan Academy of Agricultural Sciences in China and Kiyosawa in Japanese,respectively.The five Japonica landrace varieties in Taihu lake area,including Hekezijing,Bodao,Tieganqing,Jiangnanwan and Queemuo,were inoculated with Chinese forty-four blast isolates and seven Japanese differential strains in order to illustrate their resistance to various blast strains.It was showed that the twenty-six Chinese blast isolates varied with a degree of 14.8%,much higher than Japaniese strains with only 3.6%.It suggested that Japaniese strains were more stable in their virulence due to continous selection and identification in differentials with single resistance gene,and suitable for research on the resistance resource selection and genetics to blast.Meanwhile it was found that there was a high frequency of resistance to rice blast isolates in five Japonica landraces in Taihu lake area, from 88.6%to 97.7%.Among them Hekezijing and Bodao were very good resources of resistance to blast,with 97.7%and 95.1%of resistance frequence.It was obtained that the seeds of F₁,F₂ and some F_2:3 lines from the crosses of five Japonica landraces in Taihu lake area with resistance to blast and susceptible variety Suyunuo.The seedlings were further inoculated with Chinese blast races ZG₁ and ZE₃ and Japanese blast differential strain Hokul,to analysis the resistance genetic pattern of various landraces in Taihu lake area to blast.The results showed that the resistance to Hokul in Hekezijing,Bodao,Tieganqing and Queernuo may be controlled by one dominant gene,but Jiangnanwan may be by two interaction-inhibiting genes;to ZG₁ in Hekezijing and Tieganqing may be controlled by one dominant gene,and in Bodao and Jiangnanwan may be by two interaction-inhibiting genes;to ZE₃ in Hekezijing, Tieganqing and Queernuo may be controlled by one dominant gene,Bodao may be by two independently dominant gene,but Jiangnanwan may be controlled by interaction-inhibiting gene.Furthermore Bodao was crossed with twelve Japanese differential varieties carrying various resistance genes to blast to estimate whether the Bodao carried a new resistance unknown gene.The F₁,F₂ seeds as well parents were inoculated with Japanese blast differential strain Hoku1.The results showed that the resistance gene of Bodao to Hoku 1 was not allelic to twelve known blast resistance genes in Japanese differential varieties and further to study the resistance gene was or not a new gene.The seeds of F₁,F₂ and some F_2:3 lines were obtained by crossing Heikezijing with Suyunuo,and the some F₆ recombined inbreed lines(RILs) obtained by means of SSD(single seed descendant) from generation of F₂.The two parents,F₁,F₂ and F_2:3 families and F₆ recombined inbreed lines were inoculated with Japanese blast differential strain Hokul and Chinese blast race ZG₁.The F₂ individuals genotype was identified according to the reaction of F_2:3 families to rice blast strains,and the resistance gene of Heikezijing was preliminary mapped by the reactions of F₂ individual genotype to rice blast strains and SSR molecule markers.The results showed that the resistance gene of Heikezijing to Japanese differential blast strain Hokul was mapped on the end of chromosome 11,and linked to SSR molecular marker RM7654 and RM144,and between the two markers with a genetic distance of 7.2cM and 10.5cM respectively,this gene was tentatively designated as Pi-hk1(t).The resistance gene of Heikezijing to Chinese rice blast race ZG₁ was mapped on the chromosome 12 near the centromere,and linked to SSR molecular marker RM277,RM511 and RM1261,and with a genetic distance of 10.5cM,11.7cM and 20.8cM,respectively,this gene was tentatively designated as Pi-hk2(t).According to the preliminary mapping,Hekezijing was crossed with four varieties with known resistance genes on the end of chromosome 11 and the F₁,F₂ seeds was inoculated with Japanese differential blast strain Hokul and the allelism tests conducted with different genes.The results showed that the resistance gene of Hekezijing to Hokul was not allelic to known blast resistance gene Pi-1,Pi-k,Pi-44(t) and Pi-lm2. The resistance gene Pi-hk1(t) of Heikezijing was fine mapped on the end of chromosome 11 according to the reactions of F₆ recombinant inbreed lines to rice blast isolates and SSR molecule markersand was linked to SSR molecular markers RM7654 and RM27381 with a genetic distance of 0.9cM and 1.6cM,respectively.According to the reactions of F₆ recombinant inbreed lines to Chinese blast isolates ZG₁ and SSR molecular markers,the resistance gene Pi-hk2(t) in Heikezijing to Chinese blast isolate ZG₁ was further mapped and linked to SSR molecular markers RM27940 and RM28166 with a genetic distance of 14.6cM and 8.4cM,respectively.