Conventional Breeding and Molecular Markers for Blast Disease Resistance in Rice (Oryza sativa L.)

Monogenic lines,which carried 23 genes for blast resistance were tested and used donors to transfer resistance genes by crossing method.The results under blast nursery revealed that 9 genes from 23 genes were susceptible to highly susceptible under the three locations(Sakha,Gemmeza,and Zarzoura in Egypt);Pia,Pik,Pik-p,Piz-t,Pita,Pi b,Pi,Pi 19 and Pi 20.While,the genes Pii,Pik-s,Pik-h,Pi z,Piz-5,Pi sh,Pi 3,Pi 1,Pi 5,Pi 7,Pi 9,Pi 12,Pikm and Pita-2 were highly resistant at the same locations.Clustering analysis confirmed the results,which divided into two groups;the first one included all the susceptible genes,while the second one included the resistance genes.In the greenhouse test,the reaction pattern of five races produced 100%resistance under artificial inoculation with eight genes showing complete resistance to all isolates.The completely resistant genes:Pii,Pik-s,Piz,Piz-5(=bi2)(t),Pita(=Pi4)(t),Pita,Pi b and Pi1 as well as clustering analysis confirmed the results.In the F1 crosses,the results showed all the 25 crosses were resistant for leaf blast disease under field conditions.While,the results in F2 population showed seven crosses with segregation ratio of 15(R):1(S),two cross gave segregated ratio of 3 R:1 S and one gave 13:3.For the identification of blast resistance genes in the parental lines,the marker K3959,linked to Pik-s gene and the variety IRBLKS-F5 carry this gene,which was from the monogenic line.The results showed that four genotypes;Sakha 105,Sakha 103,Sakha 106 and IRBLKS-F5 were carrying Pik-s gene,while was absent in the Sakha 101,Sakha 104,IRBL5-M,IRBL9-W,IRBLTACP1 and IRBL9-W(R)genotypes.As for Pi 5 gene,the results showed that it was present in Sakha 103 and Sakha 104 varieties and absent in the rest of the genotypes.In addition,Pita-Pita-2 gene was found in the three Egyptian genotypes(Sakha 105,Sakha 101 and Sakha 104)plus IRBLTACP1 monogenetic.In F2 generation,six populations were used to study the inheritance of blast resistance and specific primers to confirm the ratio and identify the resistance genes.However,the ratios in molecular markers were the same of the ratio under field evaluation in the most population studies.These findings would facilitate in breeding programs for gene pyramiding and gene accumulation to produce durable resistance for blast using those genotypes.

Pre-Breeding Genetic Diversity Assessment of Tomato(Solanum lycopersicum L.)Cultivars Based on Molecular,Morphological and Physicochemical Parameters

Appropriate knowledge of the parental cultivars is a pre-requisite for a successful breeding program.This study characterized fruit yield,quality attributes,and molecular variations of ten tomato cultivars during three consecutive generations under greenhouse conditions.Peto 86,Castle Rock,and Red Star cultivars showed the highest fruit yield(kg/plant),total phenolic compounds(TPC),and sap acidity.Principal component analysis categorized the evaluated fruit yield into three groups based on their quality attributes.A robust positive correlation appeared among traits inside each group.A positive correlation was likewise noticed between the first and the second groups.However,a negative correlation was detected between the first,the second and the third group.Molecular profiling,using seven inter-simple sequence repeat(ISSR)primers,produced 60 loci,including 49 polymorphic loci.The molecular analysis also pinpointed the highest genetic similarity(0.92)between P73 and Moneymaker,while the lowest genetic similarity(0.46)was observed between Castle Rock and Moneymaker.The cultivars P73 and Moneymaker showed the lowest genetic distance(2.24),while the highest genetic distance(5.92)was observed between Super Marmand and Peto86,on the one hand,and between Castle Rock and Moneymaker,on the other hand.The chemical analysis of fruit sap indicated the highest levels of TPC,total flavonoids,anthocyanin,ascorbic acid and total soluble solids in Peto 86 and Castle Rock cultivars.Phylogeny analysis of tomato cultivars based on morphological and molecular attributes indicated four distinct clades.Peto 86,Castle Rock,and Red star cultivars can be recommended for the tomato hybridization breeding programs in the future,with other tomato cultivars as potentially high-yielding parents.

Nucleotide Sequence Assessment of Four ORFs of Citrus Tristeza Virus: Evidence of Recombination

Citrus Tristeza Virus(CTV),usually occurs in nature as a mixture of genotypes.Six naturally infected citrus(Citrus sinensis)trees grafted on sour orange rootstock were collected from three citrus growing governorates in Egypt(Sharqia,Qalyubia and Garbia).In this study,RT-PCR,Single-Strand Conformation Polymorphism(SSCP)and nucleotide sequence analysis were used for four independent CTV genomic regions(p65,p18,p20,and p23)to detect and assess the sequence and genetic variabilities among CTV Egyptian isolates.RTPCR products(650 bp)for the CTV p23 gene obtained from the selected isolates were used for the SSCP analysis and DNA sequencing.SSCP patterns of p23 gene for individual isolates yielded different complex haplotype patterns.Nucleotide sequence analysis of p23 region amplified from six isolates under study revealed that p23 shared high nucleotide identity 98.7%with T36 isolate from USA,Florida.Phylogenetic analysis of p23 gene indicated a close evolutionary relationship between all examined isolates and Qaha isolate(T36 isolate group),suggesting that they may have originated from closely related ancestors.Nucleotide sequence analysis of the three genes located on CTV 3′-coterminal overhang,p18,p20 and p65,amplified from isolate A3,Sharqia governorate,revealed that the p18,p65,and p20 genes were related to the T3-KB isolate from South Africa with 99%–100%sequence homology.Phylogenetic relationship analysis for p65,p18 and p20 ORFs clustered the current A3 isolate with T3 genotype group.The recombination analysis identified three of six isolates from Sharqia,and Garbia as potential recombinant for p23 gene.The isolates T36 and T3 were identified as major donors for recombination events in isolate A3.Our results concluded that p23 ORF likely to be as a hotspot region for recombination and originated through recombination event.The current study indicated that recombination is an important factor for the origin of CTV strains in Egypt.

Rice(Oryza sativa L.)Breeding among Hassawi Landrace and Egyptian Genotypes for Stem Borer(Chilo agamemnon Bles.)Resistance and Related Quantitative Traits

Rice stem borer(Chilo agamemnon Bles.)is a primary insect pest of rice and is a major limiting factor to rice production.Breeding for insect-resistant crop varieties has been an economic way of integrated pest management(IPM)as it offers a viable and ecologically acceptable approach.This study was aimed to evaluate rice genotypes for their resistance against rice stem borer.Seven parental genotypes with twenty one F1 crosses were evaluated for genotypic variation in field experiments.Analysis of variance revealed significant differences for the studied traits in almost all crosses and parents.In addition,the mean squares of parents versus their crosses were signifi-cant for stem borer resistance and other associated traits.Moreover,both general combining ability(GCA)and specific combining ability(SCA)variances were highly significant for all characters studied in the F1 generation.Based on GCA,4 genotypes(Sakha101,Gz6903-3-4-2-1,Gz9577-4-1-1 and Hassawi)exhibited highly significant negative values for stem borer resistance(–0.53,–1.06,–0.18 and–0.49,respectively)indicating they are the best combiners for stem borer resistance.Based on SCA analysis,nine cross combinations showed highly significant negative effects for stem borer resistance.Similarly,the cross Giza178
Hassawi was the best combination with significantly highest value for early maturity.In addition,seven crosses showed highly significant negative SCA for plant height trait.On the other hand,for panicle length,number of primary branches/panicle,panicle weight and 1000-grain weight,seven,four,eight and six crosses showed highly significant positive SCA,respectively.The result further revealed that the non-additive dominance genetic variance was higher than the additive variance for all evaluated traits indicating that non-additive genetic variances have a role in their inheritance.The broad-sense heritability estimates were high for all the studied traits.The stem borer resistance was significantly correlated with panicle weight and 1000-grain weight,which also showed a highly significant correlation with grain yield/plant.Thus these traits can be effectively employed in a breeding program to confer resistance against stem borer infestation in rice.It was further supported by biplot analysis,which clustered these potentially important traits into two quadrants showing their importance in any future breeding program to control stem borer infestation.This study has contributed valuable information for evaluation of genetic diversity in the local rice germplasm and its utilization in futuristic rice genetic improvement programs.