Morphological Character Analysis and Signal Cryptic Speciation in Lasiodiplodia theobromae on Cashew (Anacardium occidentale L.)

Abstract

Lasiodiplodia theobromae (Pat) Griffon & Maubl. is a pathogen causing inflorescence dieback disease of cashew in Nigeria and also a common pathogen with a wide host range in the tropics and sub-tropics. The character variations in this pathogen necessitate better understanding of it towards development of management strategies. Isolates identified as L. theobromae were cultured from inflorescence dieback disease of cashew across growing ecologies of Nigeria and studied base on morphological characters. Variability in mycelial texture and colour, conidia and septa sizes and pycnidia production were recorded in this study. The Principal Component Analysis (PCA) and WARD clustering analysis identified four well-supported traits within the isolate group. Isolates within each cluster was: 2, 2, 4 and 1 respectively and isolate CDA1416 (Obollo-Afor) and CDA2924 (Idi-Ayunre) in cluster III were the most similar. Members within clusters I and II united at the semi-partial R-Square distance of 0.0294 and 0.0278 respectively. Isolate CDA2308 (Oro) was distinguished among others and signal a potential cryptic specie, differences in these isolates were supported by conidial morphology and textural variations. This understanding will form the bases for development of diseases management strategy against the pathogen.