Abstract
The existence of biotypic variations in the natural BPH populations of Bangladesh was investigated in the greenhouse / net house of Entomology Division and in the laboratory of Biotechnology Division, BRRI, Gazipur during the year 2009 to 2013. Twenty one BPH populations, collected from rice fields of 18 different districts of the country were used to investigate the biotypic status. Four separate tests namely Screening, Preference, Honeydew and Population development for each BPH population, were performed to detect the phenotypic response of differential rice varieties to different BPH populations for their biotypic variations. Nine differential varieties having different resistant genes namely; Mudgo, ASD7, Rathu Heenati, Babawee, ARC 10550, Swarnalata, T12, Chinsaba, Pokkali, and two checks, T27A (local resistant check) and TN1 (susceptible check), were used for each test. Cluster analyses were used to group BPH populations into dendrograms based on phenotypic response obtained from screening (score as binary data) and preference tests. Fourteen BPH populations with diverged geographical background were selected for further studies from four clusters. The responses made by BPH populations in screening, preference on feeding, honeydew excretion, population development on differential rice varieties varied from each other based on their virulence / biotypic status. However, low p value in Brown-Forsythe test implying that the first three phenotypic tests, gave the evidence that there was biotypic variation among the test BPH populations and the resistance / susceptibility reaction of BPH populations to differential rice varieties revealed changing or shifting pattern to new virulent population (s). The virulent populations of BPH could be designated as different biotypes like, P20 populations as Biotype 1; P1, P8 and P23 as biotype 3; P28 as biotype 4; P4, P11 and P11A as biotype 5(t); P19 as biotype 8(b); P25 as biotype 9(b); Pgazi as biotype 10 (b); P15 as biotype 11(b); P6 as biotype 12(b) and P22 as biotype 13(b). Moreover, seventeen polymorphic microsatellite markers from the expressed sequence tags (database of BPH) were studied to confirm the BPH population structure and their biotypic status at the genomic (DNAs) level. The genomic DNAs of 14 tested BPH populations were characterized. The number of alleles per locus ranged from 2 to 9 with an average of 4.24. The band size for EST-SSR locus varied between 136 bp to 350 bp. The observed heterozygosity was low (0.160). Genetic variation was observed highest in between P1 and P15 population and that was lowest in Pgazi and P25 populations. Cluster analyses (using UPGMA method with SAHN in NTsys pc) were also used to group the test populations by constructing dendrograms based on EST- SSR markers analysis. The produced dendrogram grouped the 14 BPH populations into four diverse clusters and that were more identical with clusters of screening test. The polymorphism information content of the tested markers was high and ranged from 0.370 to 0.844 (mean = 0.620). The high cophenetic correlation (r = 0.821), between the similarity matrix and ultrametric distance matrix indicated a good representation of data in similarity matrix that produced strong dendrogram. Principle coordinates analysis also revealed significant genetic differentiation between populations of different locations. The BPH genotypes were plotted on principal coordinates 1, 2 and 3, accounting for 35.49%, 9.71% and 8.79% of the variation, respectively, and all together explaining 54% of the total variation. It could be concluded that present BPH populations of Bangladesh are of mixed populations of different biotypes. The information generated through cluster analysis based on phenotypic and enotypic data could be efficiently used in breeding program to develop BPH resistant rice varieties.