Development and utilization of susceptibility index for screening maize germplasm against shoot fly, Atherigona naqvii

Abstract

Host plant resistance is an effective and
economical approach for the management of shoot fly,
Atherigona naqvii, a major pest of spring maize in north
India. In the current study for identifying reliable resistant
sources to shoot fly from large germplasm, a new scale
for screening i.e. “Susceptibility Index” has been used
on 19 test maize inbreds. This index is based on the egg
count, per cent plant oviposited, percent deadhearts
incidence and per cent leaf injury incidence. The
genotypes were divided into three categories, six inbreds
viz. DMSC 28, HK12–6–2–4, SO1SHYQBBB13B, CM
143, Winpop 8, and CML 420 as resistant group and five
inbreds viz. LM 16, SE 563, CM 140, (CM 140 × LM
20)-2-3-1-1-1 and S87P66QBBB 30 as susceptible group
falling on the left and right side of mean susceptibility
index ± Standard deviation (S.D.), respectively. Eight
genotypes falling within the range of mean susceptibility
index ± S.D. including IIMRPPBT POOL, (CM 140 ×
LM 20)-1-1-1-2-1, (CM 140 × LM 20)-2-1-1-1-1, (CM
140 × LM 20)-1-2-2-1-1, IIMRSBT POOL, LM 20, (CM
140 × LM 20)-1-2-1-1-1 and CLQRCYQ 42 constituted
moderately resistant group. So, this index can categorize
the germplasm into discrete susceptibility classes in
comparison to the overlapping classification scale (1-9)
based on percent dead hearts alone. Moreover, as the
screening for shoot fly is carried out under natural
infestation of the pest and considering relative nature of
plant resistance, this index overcomes the limitation of the variable incidence of the shoot fly over the years and
locations.