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26. Genetic markers associated with field
resistance to leaf and neck blast across locations in rice (Oryza
sativa L.)
G.B. PRASHANTH, S. HITTALMANI, SRINIVASACHARY, K. SHADAKSHARI
and H.E. SHASHIDHAR
Department of Genetics and Plant Breeding,
University of Agricultural Sciences, GKVK, Bangalore-560065 India
Blast disease caused by Pyricularia
grisea Sacc. is the most serious fungal disease of rice (Oryza
sativa L.). One hundred and fourteen doubled haploid (DH) lines of
a cross between 1R64, an indica variety adapted to irrigated conditions
and Azucena, an upland aromatic japonica variety (Guiderdoni et
al. 1992) were used for molecular mapping of QTL associated with leaf
and neck blast resistance. The RFLP map and molecular data generated by
Huang et al. (1994) were used for QTL mapping. The DH population,
along with their parents and susceptible checks IR50, HR12 and CO39 were
screened for blast at IRRI, Philippines in 1997 and at three locations in
South India (1995) in Uniform Blast Nursery. Leaf blast was scored using
0-5 scale (Mackill and Bonman, 1992) at regular intervals from seventh day
after inoculation to transplanting date. Neck blast was scored prior to
harvest (Anonymous, 1996) in the main field. Three traits, i.e., percentage
diseased leaf area (DLA%), number of susceptible lesions (LSN) and susceptible
lesion size (LSI) were scored in all the four selected locations.
The phenotypic evaluation for blast indicated
IR64 to posses high level of leaf blast resistance across four locations.
The male parent Azucena was moderately susceptible in all the locations.
Nursery evaluation at IRRI, Philippines showed thirty two partially resistant
DH lines whereas nineteen exhibited resistance in single spore inoculation
using P06-06 isolate. Nine doubled haploid lines and IR64 showed resistant
lesions in the presence of high level of inoculum in nursery at Ponnampet
(1995), South India. Ghesquiere et al. (1996) in their study
with the same population identified few resistant lines in France using
six diverse strains of Magnaporthe grisea. Sanger et al.
(1997) observed resistant lesions on IR64 in highly favorable blast disease
environment of the Northern Hill zone of Chhatisgarh, Madhya Pradesh,
India.
Interval mapping of QTL using the
computer package MAPMAKER/QTL (Lincoln et al. 1992) with threshold
LOD »= 2.00, identified a total of twenty five QTL for leaf blast
and two QTL for neck blast resistance. Among them, fifteen QTL were detected
at blast nursery, IRRI and ten at Ponnampet. Between the two QTL identified
for neck blast resistance, Bangalore and Mudigere contributed one QTL
each (Table 1). Seventeen QTL were identified for DLA (qDLA), six QTL
for LSN (qLSN) and two QTL for LSI (qLSI). Eight QTL had major effect
(LOD »= 3.00) for leaf blast resistance (Table 1, Fig. 1). Some
of the QTL were expressed in more than one location and are presented
in Table 2, and multiple effect of chromosomal segment was hypothesized
for these QTL. These results insinuate that pleiotropism rather than close
linkage of different QTL could be the major reason why QTL for different
blast related traits were frequently detected in the same intervals across
locations. QTL on chro.# 9 controlling neck blast resistance (qNBL) in
Bangalore (LOD = 2.03, 8.5% variation) overlapped leaf blast resistance
QTL flanked by RG358-RZ12 (LOD = 2.76, 6.00% variation) of CO39/Moroberekan
recombinant inbred population screened at Ponnampet. The minor QTL for
lesion size on chro.#11 brack-eted by RG103-Npb186 flanking markers (LOD
= 2.02, 9.50% variation) partially overlapped major gene Pi-7(t)
(Wang et al., 1994) linked to RG1O3A-RG16 markers in Moroberekan,
a resistant japonica variety. The presence of QTL in one location
and itŐs absence in another indicated the differences in the pathogenic
races. While, the major QTL identified across wide geographic locations
and that too on similar chromosomal location indicates the stability of
the QTL for blast resistance. Such markers associated with QTL which are
common across locations can be used for selecting blast resistant lines.
Our study will give reliable data on stability of the molecular markers
to be used in Marker-assisted selection, map based cloning and developing
of isogenic lines for blast disease resistance.
References
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Genetics 136: 1421-1434. |