Halila, Mohamed Habib; (1994) The biology and control of wilt of chickpea caused by <italic> Fusarium oxysporum f. sp. ciceri</italic>. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Fusarium oxysporum f.sp. ciceri (FOC) was isolated from 246 chickpea plants showing symptoms typical of Fusarium wilt. Another five plants yielded Fusarium solani. FOC isolates were classified into three groups, FG3, F/SG3 and FG4 on the basis of mycelial morphology, radial growth rate and conidial dimensions. All isolates belonged to race 0 as determined by their reaction on 16 chickpea varieties. The effect of a range of inoculum densities (500, 1000, 2000 and 4000 colony forming units/gram of soil) in combination with five air temperature regimes (10, 15, 20, 25 and 30°C) on wilt incidence was studied in three susceptible chickpea varieties, ILC 223, ILC 482 and ILC 3279. The incidence of wilt increased with increasing inoculum levels and with increasing temperature up to 25°C. Kabuli chickpea varieties were screened in a wilt sick plot (WSP) and rated as susceptible when wilt incidence was ?10%. The 1,915 varieties screened were placed in four classes on the basis of the timing of the onset of wilt symptoms. These developed within a 2 week period in all four classes which were described as very early wilters, early wilters, late wilters and very late wilters depending on whether ?10% plants showed symptoms 28, 42, 56 or 70 days after emergence. In a further class disease incidence increased slowly throughout the growing season. Resistance was found in 110 varieties and these maintained their resistance in a laboratory screening procedure. Environmental variables most closely associated with rapid disease increase were high maximum daily temperature and cumulative numbers of days in which the mean temperature was ?25°C. Preliminary studies to determine the mechanism by which FOC causes wilt symptoms showed that culture filtrates of isolate FG3 and Spanish race 0 were toxic to leaf cells isolated from the plant. Maximum toxic activity was obtained when isolate FG3 was grown on chickpea seed medium for 2 weeks. Field management of FOC disease was achieved by planting chickpea varieties, which combined the characters of late wilting and early flowering, in winter so that growth of the plant was essentially complete by the time temperatures became favourable for disease development.

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