Blast resistance in the core collection of foxtail millet germplasm

1. Introduction
Foxtail millet (Setaria italica (L.) Beauv.) is one of the ten small-grained cereals (small millets),
grown as a food crop in Asia, and as animal feed in the USA and Europe. This is a short growth
duration crop, which is valued for its nutritious grain. Though resistant to most insect pests
and diseases, blast disease, caused by Magnaporthe grisea, is the only yield limiting biotic
constraint to this crop. Symptoms of the disease appear as circular spots with a straw-colored
center on the leaf blade. Node, neck and stem tissues are also infected in addition to leaf
sheaths (Fig. 1). The objective of the study discussed here is to identify sources of blast resistance
in the foxtail millet core collection, comprising 155 accessions selected from germplasm accessions
available in the ICRISAT gene bank.
Resistance to Blast in the Core Collection
of Foxtail millet Germplasm
Rajan Sharma, AG Girish, HD Upadhyaya, VP Rao, P Humayun, TK Babu, RP Thakur
Materials and Methods
Pathogen isolates. Cultures of M. grisea were established from diseased samples collected from the
foxtail millet fields in the 2008 rainy season from Patancheru, Nandyal, Vijayanagaram and Mandya,
India. Isolations were made from the diseased samples on oatmeal agar (OMA) medium and the
pathogen was purified through single-spore isolation.
Field evaluation of foxtail millet core collection for blast resistance. Foxtail millet core collection
comprising of 155 accessions along with 4 checks (ISe 375, -376, -1468 and -1541) was evaluated at
ICRISAT-Patancheru in a RCBD with 2 replicates, 1 row of 2 m long/replicate for leaf, neck and head
blast resistance during 2009 and 2010 rainy seasons following artificial inoculation of 30 days old
plants with Patancheru isolate of M. grisea.
Confirmation of leaf blast resistance under greenhouse conditions. Accessions were further
evaluated under greenhouse conditions. The 15-day-old potted seedlings were spray-inoculated
with an aqueous conidial suspension (1×105
conidia ml-1
) of Patancheru isolate of M.grisea multiplied
on OMA medium at 27±1ºC for 7 days. Inoculated seedlings were incubated at 23°C with >95% RH
and leaf wetness under 12 h photoperiod for 7 days.
Identification of blast resistance to different populations of M. grisea adapted to foxtail millet.
Twenty-six accessions (20 resistant to neck and head blast under field conditions during 2009 and
2010, and six to leaf blast in the greenhouse screen) were further screened for leaf, sheath, neck
and head blast resistance against four isolates collected from four locations along with germplasm
checks (ISe 376 and -1541) and susceptible check (ISe 1118). The experiment was conducted in a
CRD with 2 replicates, 1 pot/replicate, and five plants/pot.
For leaf blast reaction, 15-day-old seedlings were inoculated, and for sheath, neck and head blast,
accessions were spray inoculated at anthesis stage.
Data recording
•• The leaf blast severity was recorded at 10 DAI using a progressive 1-9 scale; where 1 = no lesions to
small brown pinhead size specks, and 9 = >75% leaf area covered with lesions or all the leaves dead.
•• A 1-5 progressive rating scale (1 = no lesions to pin head size of lesions on the neck/sheath region,
2 = 0.1 to 2.0 cm, 3 = 2.1 to 4.0 cm, 4 = 4.1 to 6.0 cm and 5 = >6.0 cm of lesions on the neck/sheath
region) was developed for recording the neck and sheath blast severity at physiological maturity.
Neck blast incidence in the field screen was recorded as a percentage of infected plants having
neck blast at maturity.
•• Head blast incidence was recorded as a percentage of infected heads at maturity.
Results
•• All the 155 accessions recorded ≤10% head blast incidence in the field. One hundred fifty one
accessions recorded a score of ≤3.0 for leaf blast compared to 4 accessions (ISe 1129, ISe 1299,
ISe 1037 and ISe 1118) that scored ≥7 on a 1-9 scale under field conditions (Fig. 2).
•• Twenty accessions from the core collection (ISe 375, -748, -751, -769, -771, -785, -846, -1067,
-1137, -1204,-1286, -1320, -1335, -1387, -1419, - 1547, -1563, -1593, -1685 and -1704,) and two
check lines (ISe 376 and - 1541) were resistant (≤10% incidence) to neck and head blast in both
2009 and 2010 in the field.
•• Only 15 of the 155 accessions were found resistant (score ≤3.0) and 20 moderately resistant (score
3.1 to 5.0) to leaf blast in the greenhouse screen.
•• Differentialleafblastreactionwasobservedintheselectedfoxtailmilletaccessionswhenscreened
against four isolates of M. grisea (Table 1).
•• Two accessions (ISe 1547 and ISe 1181) were free from head blast and resistant to leaf (score ≤3.0
on 1-9 scale), neck and sheath blast (score ≤2.0 on 1-5 scale) against all the four test isolates. In
addition, ISe 1067, -1563 and -1575 were also found promising for blast resistance (Table 1).
Conclusions
•• Reaction of foxtail millet accessions to four isolates revealed pathogenic variation in the M. grisea
populations adapted to foxtail millet in India.
•• Two accessions, ISe 1547 and ISe 1181, were found resistant to leaf, neck, sheath and head blast
against all the four isolates, and could be used as potential sources of blast resistance in the
foxtail millet improvement program in India.
Table 1. Evaluation of selected accessions of foxtail millet core collection for leaf, neck, sheath and head blast
against four Magnaporthe grisea isolates under greenhouse conditions, December 2011 – April 2012.
Accession
(Ise) No
Leaf blast (1-9 scale) Head blast (%) Neck blast (1-5 scale) Sheath blast (1-5 scale)
Fx57 Fx58 Fx60 Fx62 Fx57 Fx58 Fx60 Fx62 Fx57 Fx58 Fx60 Fx62 Fx57 Fx58 Fx60 Fx62
375 3.0 3.0 4.0 2.0 0.0 40.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
376* 2.0 3.0 4.0 3.0 0.0 80.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
748 6.0 5.0 7.0 6.0 0.0 0.0 0.0 0.0 1.1 1.0 1.1 1.0 1.0 1.5 1.2 1.0
751 4.0 5.0 5.0 6.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.3 1.0 1.2 1.0
769 5.0 5.0 6.0 4.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
771 9.0 8.0 8.0 8.0 0.0 0.0 0.0 0.0 1.0 1.4 1.0 1.0 1.0 2.7 1.8 1.8
785 9.0 8.0 8.0 8.0 0.0 10.0 0.0 20.0 2.1 1.0 1.0 1.0 3.9 3.7 1.4 1.7
846 8.5 6.0 7.0 6.0 0.0 50.0 0.0 0.0 1.0 2.8 1.0 1.0 1.0 2.2 1.0 1.3
1059 3.0 5.0 5.0 3.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
1067 2.0 3.0 4.0 2.0 0.0 0.0 0.0 0.0 1.0 1.1 1.2 1.0 1.0 1.0 1.0 1.0
1137 8.5 4.0 4.0 3.0 20.0 0.0 0.0 60.0 1.0 1.1 1.0 1.4 2.0 2.2 1.4 2.8
1181 1.0 3.0 3.0 3.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
1187 3.0 3.0 3.0 4.0 0.0 0.0 0.0 50.0 0.0 0.0 0.0 50.0 0.0 0.0 0.0 5.0
1201 2.0 4.0 6.0 3.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
1204 6.0 4.0 3.0 3.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
1258 2.0 8.0 7.0 7.0 0.0 0.0 25.0 0.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
1286 6.0 7.0 6.0 5.0 100.0 83.3 80.0 40.0 4.4 3.7 3.7 2.0 4.5 4.4 4.2 3.0
1320 5.5 5.0 6.0 6.0 0.0 0.0 0.0 0.0 1.0 1.6 1.0 1.0 1.5 2.0 1.4 1.0
1335 9.0 7.0 6.0 5.0 12.5 0.0 20.0 0.0 1.0 1.1 1.2 1.0 2.4 2.8 3.3 1.9
1387 8.0 6.0 5.0 7.0 0.0 0.0 – 0.0 1.0 1.0 – 1.0 1.0 1.8 – 1.0
1419 4.0 3.0 3.0 7.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.1 1.1 1.0 1.0 1.0
1541* 3.0 3.0 4.0 3.0 0.0 60.0 60.0 60.0 1.0 1.0 2.3 1.0 1.3 1.0 3.5 2.7
1547 3.0 3.0 2.0 3.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 2.0 1.5 1.0 1.0
1563 3.0 4.0 2.0 3.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 2.0 1.6 3.0 1.1
1575 2.0 3.0 4.0 3.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.2 1.0 1.0 1.1
1593 4.0 5.0 5.0 5.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.2 1.0 1.0 1.0
1685 3.0 9.0 8.0 8.0 0.0 0.0 0.0 0.0 1.0 1.0 1.0 1.0 1.2 1.4 1.6 1.0
1704 8.0 9.0 8.0 8.0 0.0 0.0 30.0 0.0 1.1 1.0 1.0 1.4 2.5 1.7 1.9 2.5
1118 9.0 8.0 7.0 6.0 100.0 100.0 62.5 100.0 4.7 4.6 3.5 3.7 4.5 4.9 4.0 3.6
Isolate
mean 4.7 5.0 5.1 4.8 4.7 11.5 8.0 8.2 1.1 1.2 1.1 2.8 1.5 1.6 1.5 1.5
* Germplasm checks; – No germination
Fx57 =Patancheru isolate
Fx58 = Nandyal isolate
Fx60 = Vizayanagaram isolate
Fx62=Mandya isolate
Figure 1. Symptoms of foxtail millet blast in the greenhouse screen:
a. Leaf and neck blast; b. sheath blast; c. head blast.
Figure 2. Summary of disease reaction of foxtail millet core collection for leaf, neck and head blast under
field conditions at Patancheru.
Resistant: ≤3.0 score for leaf blast and ≤10% neck and head blast incidence
Moderately resistant: 3.1 to 5.0 score for leaf blast and 11 to 30% neck and head blast incidence
Susceptible: 5.1 to 7.0 score for leaf blast and 30 to 50% neck and head blast incidence
Highly susceptible: >7 score for leaf blast and >50% neck and head blast incidence
Sep-2012
a b c
Resistant to leaf, sheath, neck and head blast against all the four isolates
Resistant to three and moderately resistant to fourth isolate
Susceptible check