Distribution, Severity, and Spread of Armillaria Root Disease in Kenya Tea Plantations

Abstract

Surveys for Armillaria root disease severity were conducted over a 5-year period in small tea farms (0.5 to 1.0 ha) in the 12 tea-growing districts of Kenya. The disease occurred in all tea districts, but severity was greater in the districts east of the Rift Valley. Disease severity was associated with relative amounts of residual woody debris, especially roots, from trees and shrubs present when the land was converted to tea plantations. Excavation of tea bushes in disease centers showed that infection of tea bushes occurred primarily by mycelial growth from residual tree roots and from infected tea roots rather than from rhizomorphs. Rhizomorphs were scarce, and rarely involved in infection. They were confined mostly to the surface of the residual tree roots and were found growing freely in the soil in only one tea district. Rhizomorphs were more abundant in higher elevation plantations than in lower elevation plantations, where they occurred only on residual tree roots in the deeper, cooler, moister levels of the soil. Inoculum from residual tree debris in the soil was the most important source of infection in plantations of seed origin. Secondary spread from infected tea plants to healthy ones was limited and disease centers were small. In tea plantations derived from clonal cuttings, secondary disease spread from infected to healthy tea plants was more important resulting in large disease centers or gaps due to plant death and removal. Currently, soil sanitation by thorough removal of roots of forest trees and prompt removal of infected tea bushes is the best available management practice.

Incidence and phylogenetic analyses of Armillaria spp. associated with root disease in peach orchards in the State of Mexico, Mexico

“…3.1 m between plants and 4.3 m between rows. To maintain productivity in established peach orchards, it is critical to develop and adopt management practices to diminish impacts of Armillaria root disease, such as reducing inoculum sources before planting or in established orchards (Onsando et al 1997;Cox et al 2005;Prodorutti et al 2009) and development of resistant rootstock, among other measures. Previous studies have indicated that A. mellea disperses mainly by rhizomorphs in pear orchards (Rizzo et al 1998).…”

Effects of inoculum potential, shading and soil temperature on root infection of oil palm seedlings by the basal stem rot pathogen Ganoderma boninense

“…The occurrence of upper stem rot (USR) where decay occurs higher up the stem (above 1–1·5 m) and can cause palms to break in two, is much less frequent. There has been a general consensus within the industry that the primary route of infection for BSR is through roots, as is the case with other basidiomycete root‐invading pathogens, notably Heterobasidion annosum (Woodward et al ., 1998), cause of root and butt rot of conifers in temperate regions and Armillaria spp., which are pathogenic to numerous tree species (Onsando, 1997). Thus, any woody material colonized by G. boninense is a potential source of inoculum for the current stand and any colonized debris left from one stand might provide inoculum for the next planting (Hasan & Turner, 1998).…”

Antifungal activities of Chaetomium spp. against Fusarium wilt of tea

“…With a 1% loss of bushes which is owed to root disease, in the 10 th years the loss of the potential crop would be 10% (Hainsworth 1952). In Kenya, the loss of tea bushes caused by root disease could reach up to 50% (Onsando et al 1997).…”