d(GC) - Association of Biotechnology and Pharmacy

Current Trends in Biotechnology and Pharmacy
Vol. 6 (2) 173-182 April 2012, ISSN 0973-8916 (Print), 2230-7303 (Online)
Genetic frequency for heterozygsity in the
population was analyzed using Hardy-Weinberg
equilibrium it was revealed that few
heterozygote’s was observed indicating
inbreeding pattern in the population this may be
due to the most of the isolates collected from
same region while MGM - 2, MGM - 5 and MGM
– 24 primers showed significant observed
heterozygosity (Table 2) indicating that MGM
primers are the right choice to analyze the
Magnaporthe grisea genetic diversity compared
to other conventional primers, Similarly using
Hardy–Weinberg equilibrium Li et al., (29) was
observed no deviations between any pair of loci,
suggesting that null alleles at all the loci are rare
in M. grisea. However, we observed great extent
of variation among the isolates collected from
different endemic areas. For instance, the
isolates collected from Mareturu (SP 25 and SP
26), Assam (SP 3 and SP 4), Almora (SP 1 and
SP 2) and Nellore grouped in the same cluster
but they share only 35 % similarity. Another 9
isolates two each from Ranchi (SP 33 and SP
34), Jagityal (SP 20 and SP 21), Karjat (SP 22
and SP 23) and 3 isolates from DRR (SP 12, SP
10 and SP 19) also grouped in the first major
cluster they were out grouped with two sub
clusters by showing 75 % dissimilarity to the
isolates in the first major cluster. We also
observed some exceptions like isolates collected
from coastal Andhra Pradesh (Mareturu and
Nellore) shares the high similarity of 64 % with
Assam isolates (SP 3 and SP 4). High similarities
between isolates collected from various endemic
areas of India like Uttaranchal, Himachal Pradesh
those of Madhya Pradesh and Karnataka was
reported earlier by Chadha et al., (30) with RAPD
markers contributing to the possibility of seedborne
transmission of the pathogen. Therefore
it is expected that, the migration of the pathogen
to a newer location operates. Due to extensive
gene flow among the isolates genetic variability
may arise that was evident from the presence of
high variation among the isolates collected from
different endemic areas. Kumar et al., (23) also
179
concluded the migration of the pathogen that
results in to the wide distribution of lineages in
the Indo-Gangetic Plains of India. Nguyen et al.,
(31) also observed the significant gene flow
between P. oryzae isolates of indica populations
collected from North Vietnam.
The clustering analysis revealed the grouping
of the isolates collected over differentials with the
isolates collected from the susceptible cultivars
of blast endemic areas. Based on these
clustering and similarity values, a prediction of
AVR/avr genes was done. The isolate (SP 14)
which was virulent on differential variety i.e.,
Kanto51 (which has Pi-k gene) shares 43 %
similarity with the isolates (SP 29 and SP 30)
collected from Nellore. Hence, we presumed that
in Nellore region the fungal population may have
avr Pi-k gene, hence deployment of varieties
having Pi-k gene may not offer resistance to this
prevalent race in that region. Interestingly, many
present day ruling varieties (NLR 145) in this
region have developed using Tetep (which has
Pi-Kh ) as a resistance source (32, 33). It is also
predicted that there will be many alleles exist in
avr Pi-k cluster in Magnaporthe grisea as like Pik
cluster in rice It has also been reported that
the Pi-k locus is actually a cluster of genes
including Pik-p, Pik-m, Pik-s and Pik-h present
on rice chromosome 11 (34). Similarly, the isolate
(SP 24) collected from endemic area of South
India (Mandya- Karnataka) showed 70 %
similarity with the isolate (SP 17) which is
collected on IR50 variety as well as 40 % with
the isolate (SP 9) which is collected on BL-245
variety which is known to contain a combination
of Pi-2 and Pi-4 genes. Hence the fungal
population of Mandya region might be having
both or either of avr Pi-2 and avr Pi-4 genes.
Assam fungal population might be having avr
Pi-ks gene since these isolates collected from
these regions showed 64 % of similarity to the
isolate collected from a differential variety
(Calaro) which contains Pi-ks gene. On the other
hand, tightly linked blast resistance genes at the
Pik locus were presumed to have evolved from
Analysis of Population Structure of Magnaporthe grisea