Ecological Factors Influencing Severity of Cashew Fusarium Wilt Disease in Tanzania

Abstract

Cashew (Anacardium occidentale L.) is an important cash crop in Tanzania as a source of income to cashew growers and provides foreign exchange for the country. Despite its significance, the crop is threatened by fast spreading disease known as cashew Fusarium wilt caused by Fusarium oxysporum. Field assessment and laboratory tests were conducted to determine incidences of the disease, severity, ecological factors that influence them and explored the pathogen host specificity in six cashew growing districts. The results revealed significant (P<0.001) variation of disease incidences and severity among the studied districts. The results further revealed that there is both positive and negative correlation between the incidence and severity of the disease versus the evaluated ecological factors. The soil pH, soil temperature, air temperature, and relative humidity depicted positive correlation of disease incidence and severity versus ecological factors at ρ=0. 50 and ρ=0.60, ρ=0.20 and ρ=0.94, ρ=0.11 and ρ=0.812, ρ=0.05 and ρ=0.771 respectively while nitrogen, phosphorus, and carbon depicted negative correlations at ρ=-0.22 and ρ=-0.58, ρ=-0.15 and ρ=-0.94, ρ=-0.19 and ρ=-0.12 respectively. In terms of host range, none of the weed species was found to be a carrier of Fusarium pathogen implying that it is host specific or semi selective. The results revealed that the tested ecological parameters favor the growth and development of Fusarium pathogen. Thus, management of the disease requires nutrients replenishment and soil shading as essential components in developing appropriate strategies for the control and prevention of further spread of the disease.

Potential of LocalBacillusspp. Isolates as Wilt Disease Biocontrol Agents forFusarium(Fusarium oxysporumf. sp.cepae) on Wakegi Onions (Allium×wakegiAraki)

“…The intensity of the disease was calculated from the onset of symptoms at an interval of 7 days. The percentage of disease incidence was calculated using the formula proposed by Shamyuktha et al [28] and Lilai et al [29].…”

“…The percentage of disease incidence was calculated using the formula proposed by Shamyuktha et al [28] and Lilai et al [29].…”

“…Bacillus subtilis bacteria were known to produce lipopeptide compounds that were antibiotic and had a broad spectrum, such as iturin, surfactin, and fengysin [54,14,56)]. These compounds have shown potential antagonistic activity against pathogenic bacteria and fungi in both in vitro and in planta conditions to suppress disease incidence and severity [14,29].…”