Abstract:
Chickpea (Cicer arietinum L.) is the most important pulse crop among the major
Rabi pulses of Pakistan. Fusarium wilt which is caused by Fusarium oxysporum f. sp.
ciceris is considered to be the most devastating disease of this crop. Survey for the
assessment of chickpea wilt disease was conducted in February - March 2005 and 2006 of
major chickpea growing areas of Pakistan. During this survey, maximum disease
prevalence (92.58 ± 3.69), incidence (82.52 ± 5.14) and severity (7.00 ± 0.48) was
recorded in the districts Khushab, Bhakkar, Layyah, Mianwali and Sargodha. The lowest
disease prevalence (29.70 ± 3.19), incidence (9.50 ± 1.72) and severity (2.1 ± 0.10) was
recorded in districts Jafarabad, Dera Allah Yar, Attock, Peshawar, Rawalpindi / Islamabad.
A strong correlation between disease incidence and climatic conditions in all districts was
observed.
Pathogenesis studies of these isolates were done in order to correlate
epidemiological factors of chickpea wilt. Studies showed that seedling mortality was
minimum at 3g inoculum concentration and maximum at 20g. Similarly, seedling mortality
was maximum in sandy soil and minimum in clayey soil. Whereas, at low level of soil
moisture disease severity was maximum and at high level it was minimum. The effect of
disease development on the sap extract of leaves and roots showed maximum growth on
root sap then leaves.
In physiological studies the fungus grew best on Waksman Agar (WA) medium and
least on Potato Dextrose Agar (PDA) medium. Glucose was found to be the best and
mannitol least carbon source. Similarly potassium nitrate (KNO 3 ) was the best and
ammonium sulphate (NH 4 ) 2 SO 4 was least nitrogen source. Growth of F. oxysporum was
maximum at 30 0 C after 7 days of incubation, which reduced drastically below and above this
temperature. Similarly, the fungus growth was best at pH 7; below and above this pH it was
reduced.
In case of pathogenic variability of 10 chickpea genotypes the most virulent isolate
was Foc-15 (Bannu) and the least virulent was Foc-17 (Fateh-Jang) from 27 F. oxysporum
f. sp. ciceris isolates. The remaining isolates showed intermediate response of variation in
virulence. Cultivar ICCV2 (1±0.0) was found resistant and AUG-424 (9.0±0.0) susceptible
xivagainst all the isolates. On morphological and cultural basis the isolate Foc-9 (90 mm) was
found fast growing whereas, isolate Foc-22 (39 mm) was slow growing. The rest of
isolates remained intermediate. The biggest size of the micro-conidia (3.7 x 4.5 μm) was
obtained from the isolate Foc-14 and the smallest size (2.7 x 4.7 μm) from isolates Foc-2.
Similarly the largest macro-conidia were obtained from the isolates Foc-6 (6.5 x 17.5 μm)
and the smallest from isolates Foc-25 (7.5 x 20.1 μm). Maximum dry mycelium weight
was obtained from isolate Foc-21 (1.56 g) and minimum from Foc-22 (0.31g). Sensitivity
of F. oxysporum f. sp ciceris isolates to thirteen fungicides @ 100 ppm was observed.
Benlate was found most effective fungicide against all the isolates in suppressing the
fungal growth under test. The least effective fungicide were Captan and PCNB. The rest of
fungicides showed intermediate response. In case of mycelial compatibility grouping out of
350 combinations only 91 combinations showed compatible reactions, whereas, 259 were
identified as non-compatible.
To identify genetic sources of resistance against wilt disease under artificial disease
conditions in three consecutive years (2005, 2006 and 2007), 553 germplasm lines were
screened. Disease observations were recorded from seedling to reproductive stages. At
seedling stage, 233 genotypes were found resistant, 102 tolerant and 218 susceptible.
Whereas, at reproductive stage 125 lines were resistant, 53 tolerant and 375 were observed
susceptible.
To evaluate the genetic relationship in the morphological traits and RAPD markers
genetically diverse 38 chickpea genotypes were selected, which provided ample
opportunity to create favorable gene combinations. 35 Random amplified polymorphic
DNA (RAPD) markers were used to assess genetic diversity in comparison with agro-
morphological traits. Agro-morphological traits have given significant results among
genotypes. Days to 50% flowering ranged from 92-112, plant height ranged from 54.2-
87cm, Primary and secondary branches per plant varied from 1.4-6 and 4-20, pods per
plant varied from 8-34, whereas grain yield per plant ranged from 3.47-10.2g. Disease was
scored against the test genotypes, which, was recorded on 1-9 rating scale. The cluster
analysis for the phylogenetic relationship among genotypes on the basis of agro-
morphological traits revealed three distinct groups at 92% similarity level.