Diversity in Fusarium oxysporum f.sp. ciceris causing vascular wilt disease in chickpea

1. Diversity in Fusarium oxysporum f.sp. ciceris causing
vascular wilt disease in chickpea
A Nagavardhini, M Sharma and S PandeA Nagavardhini, M Sharma and S Pande
Introduction
 Fusarium wilt [Fusarium oxysporum f. sp. ciceris (Padwick) Matuo & K. Satô (Foc)] is the most important
disease of chickpea, worldwide.
 It can cause 100% yield losses in susceptible cultivars annually (Fig. 1)
 Foc is highly variable and frequent recurrences of its virulent forms have limited the efficiency of
resistant cultivars in disease management.
 Diversity studies in Foc population will help in developing location specific resistant varieties of
chickpea and their strategic deployment in marker-assisted breeding.
Fig. 1. Fusarium wilt infected chickpea field, (inset) split root and shoot showing discoloration of xylem vessels.
Objectives
 Characterize the phenotypic diversity in the F. oxysporum f.sp. ciceris isolates collected from diverse
geographical regions of India.
 Assess virulence diversity of Foc isolates using host differentials.
 Determine the race scenario of Foc in India.
Materials and methods
Collection of isolates
 Total isolates collected: 274 from 27 districts located in 14 states of India during 1995-2010 .
 Isolates single spored and maintained on Potato Dextrose Agar (PDA) at 4°C.
Pathological diversity
 The pathogenicity for 274 Foc isolates was proved on the wilt susceptible chickpea cultivar ICC 4991
(JG 62) in a greenhouse using the root dip inoculation technique.
Cultural & morphological diversity
 Colony color, diameter, pigmentation, morphometric measurements and formation of conidia and
chlamydospore production assayed on PDA at 25°C.
Virulence diversity
 Virulence reaction of monoconidial Foc isolates on 10 standard chickpea differentials ((JG62, JG74,
Chafa, WR315, L550, BG212, CPS1, C104, Annigeri and K850) studied under greenhouse conditions
following root dip inoculation technique.
Results
Pathological diversity
 Of 274 Foc isolates, 196 were pathogenic and 78 non-pathogenic (Table 1).
 Significant variation in incubation period (11-48 days) and latent period (15-53 days) found.
 98 FOC isolates representing diverse geographical locations (27 districts located in 14 states of India)
selected for diversity studies (Fig. 2).
Table 1 : Pathological diversity in Foc isolates
State Isolates
collected
(No.)
More
virulent
isolates
(No).
Less
virulent
isolates
(No.)
Non
pathogenic
isolates
(No.)
Andhra Pradesh 47 30 9 8
Madhya Pradesh 67 19 25 23
Himachal Pradesh 17 7 3 7
Karnataka 11 8 2 1
Chattisgarh 70 7 39 24
Uttar Pradesh 15 8 3 4
Delhi 6 6 0 0
Haryana 5 5 0 0
Gujarat 8 6 0 2
Maharashtra 6 4 1 1
Punjab 4 3 0 1
Bihar 3 1 2 0
Near Nepal 3 1 2 0
Uttarakhand 9 3 2 4
Jharkhand 3 0 0 3
Total isolates 274 108 88 78
Cultural and morphological diversity
 Significant variations in colony morphology (Table 2 & Fig. 3) and spore morphology (Table 3 & Fig. 4)
of Foc isolates found.
 Chlamydospores mostly produced profusely and singly at intercalary positions on growing hyphae and
absent in some cases.
 Chlamydospore development varied in different isolates from 2-5 weeks.
Fig. 2. Representative isolates from diverse
geographical regions of India used for diversity
studies
Fig. 3. Cultural diversity of Foc isolates.
Fig. 4. Morphological diversity in Foc isolates.
Table 2: Cultural diversity in Foc isolates
Colony character Group (No. of isolates)
Colour
White (61), off-white (10), Light pink(18), pale violet
(4), light yellow (2), light orange (3)
Texture
Fluffy & abundant (50), Partially fluffy & sparse(15),
appressed & abundant(18), appressed & sparse(15)
Pigmentation
White(38), Pale-dark yellow(31), Pale-dark pink(10),
Orange(15), Pale -dark violet(4)
Average growth
rate/day
0.46 to 1.13 cm.
 Occurrence of new pathogenic races of Foc in major chickpea growing regions of India, and existence
of multiple races at one place, was found.
 The race reaction of Andhra Pradesh, Uttar Pradesh, Punjab, Haryana and Madhya Pradesh isolates
differed from the race reaction as reported earlier.
 Race 6 reported from California and Mediterranean basin found in Madhya Pradesh, Uttar Pradesh,
Punjab and Delhi.
Conclusion
 Significant diversity in Foc isolates in different agroclimatic regions of India recorded .
 Changed race scenario of Foc found, and existence of new and multiple races found in one region.
 Continuous monitoring of changes in race scenario of Foc is needed to anticipate the breakdown of
wilt resistance and deployment of multirace-resistant genotypes.
Fig. 5. Virulence diversity in Foc isolates in AP state.
065 070 075 080 085 090 095 100
Table 3: Morphological diversity in Foc isolates
Type Shape Size (µm) Septa No. conidia/cm
2
Microconidia Oval, ellipti-
cal or kidney
shaped
4.3 - 9.9 ×
1.6 - 3.9
0-1 2.0 × 10
5
- 8.7 ×
10
6
Macroconidia Straight to
slightly curved
13.0 - 34.9
× 1.5 - 5.2
3-5 7.9 × 10
4
- 1.2 ×
10
6
Chlamydospore Mostly oval,
Smooth or
rough walled
- - Abundant (in
most ), few
(some), absent
(some)
Virulence diversity
 Greater diversity in Foc isolates in different region
observed (see. Fig. 5).
 Cluster analysis based on disease incidence grouped 98
isolates in to 11 major pathogenic clusters (Fig .7).
 All the clusters included isolates from different regions.
 The results indicate the changing scenario of Foc races in
India (Fig. 6).
Fig. 6. Changing scenario of Foc races in India.
Fig. 7. Average linkage cluster analysis of of Foc isolates
based on disease incidence.
Nov 12