Abstract
Leaf-blight disease of Colocasia caused by Phytophthora colocasiae Raciborski has been a serious impediment to cocoyam production in Nigeria. Disease severity and susceptibility of the two most cultivated local varieties “Ugwuta” (Colocasia esculenta var. antiquorum) and “Nkashi Colocasia esculenta var. esculenta) were investigated. Disease severity was visually estimated as the percentage leaf surface affected by blight, lesion or lesion-related chlorosis for each leaf of a plant using a seven-point scale of 0, 5, 10, 25, 50, 75 and 100% in three locations: Ede-Oballa, Nsukka Urban and Obukpa. Susceptibility was assessed on 2 months old potted plants of each variety inoculated with a 7-day old culture of P. colocasiae. Diameters of lesions on inoculated leaves were recorded from the 3rd - 8th day after inoculation. Data on severity were subjected to ANOVA and susceptibility of the varieties was compared with t-test. Results revealed significant LSD=4.96 (0.05) and varying degrees of leaf blight severity among varieties and locations. Variety antiquorum had significantly higher severities of 42.08, 46.40 and 47.42% at Ede-Oballa, Nsukka Urban and Obukpa respectively, compared to 34.85, 36.55 and 28.19% recorded by var. esculenta at these locations, respectively. Similarly, var. antiquorum had greater lesion diameter ranging from 0.65±0.07 cm - 3.70±0.14 cm and average diameter of 2.4±0.16cm compared to var. esculenta which had 0.41±0.14cm - 3.12±0.19 cm and average diameter of 1.80±0.16. This research has shown that varieties and locations affect the severity and susceptibility of Phytophthora leaf blight disease. This could be a guide to farmers having known that var. esculenta is less severe to Phytophthora leaf blight disease.
Highlights
Taro (Colocasia esculenta (L.) Schott) is a herbaceous perennial plant in the sub-family Colocasioideae of the monocotyledonous Aroids
Trial was conducted in the screen house with meteorological section of the department of crop potted taro plants to determine the susceptibility science, University of Nigeria, Nsukka were of the two varieties to P. colocasiae
The interactive effects of variety and location on disease severity as presented in Table 1 revealed that TLB severity was significant LSD=4.96 (0.05) and more severe in var. antiquorum than in var. esculenta in all the locations
Summary
Taro (Colocasia esculenta (L.) Schott) is a herbaceous perennial plant in the sub-family Colocasioideae of the monocotyledonous Aroids. Hong et al (2021) stated that taro leaf blight, caused by a severely destructive Oomycete fungus Phytophthora colocasiae, is responsible for threatening yield loss worldwide. In the presence of a virulent pathogen, disease may or may not occur depending on the susceptibility of the host and the suitability of the environment Each of these components is subject to a considerable variation and as one component changes it can affect disease severity. Nsukka zone is one of the major taro producing areas in Nigeria located north of Enugu State. This zone has exhibited differential response to the TLB scourge with respect to disease incidence among taro varieties and locations since the inception of the disease (Chiejina and Ugwuja, 2013).
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