Relationship between incidence and severity of cashew gummosis in semiarid north‐eastern Brazil

Abstract

The incidence–severity relationship for cashew gummosis, caused by Lasiodiplodia theobromae, was studied to determine the feasibility of using disease incidence to estimate indirectly disease severity in order to establish the potential damage caused by this disease in semiarid north‐eastern Brazil. Epidemics were monitored in two cashew orchards, from 1995 to 1998 in an experimental field composed of 28 dwarf clones, and from 2000 to 2002 in a commercial orchard of a single clone. The two sites were located 10 km from each other. Logarithmic transformation achieved the best linear adjustment of incidence and severity data as determined by coefficients of determination for place, age and pooled data. A very high correlation between incidence and severity was found in both fields, with different disease pressures, different cashew genotypes, different ages and at several epidemic stages. Thus, the easily assessed gummosis incidence could be used to estimate gummosis severity levels.

Epidemiology of cashew anthracnose (Colletotrichum gloeosporioides Penz.) in Mozambique

“…Incidence and severity were evaluated simultaneously based on the standardized leaf damage scale developed for cashew powdery mildew (Nathaniels, 1996). In this study, severity described the percentage of necroticised leaf area while incidence reflected the percentage of diseased leaves (McRoberts et al, 2003;Cardoso et al, 2004). Later in each crop season, anthracnose incidence on the nuts was also assessed as percentage of symptomatic immature nuts/panicle/plant.…”

“…Severe damage on adult plants results in defoliation during shoot development, death of inflorescences and later necrosis and falling of immature nuts (Freire and Cardoso, 2003). Damage assessment can therefore be done at any of the above stages depending on the purpose of the evaluation, which can be fungicide (Da Matta and Lellis, 1973) or germplasm screening (Cardoso et al, 1999), or epidemiological investigations (McRoberts et al, 2003;Cardoso et al, 2004). In any of the above approaches, terminology such as disease incidence, disease severity, disease density and others are commonly used to measure the disease.…”

“…Many other authors (Silva-Acuna et al, 1999) have however found simple, consistent and useful relationships in different pathosystems. Tedious and time consuming work associated with severity measurement has been replaced by the easily measured incidence (Silva-Acuna et al, 1999;Cardoso et al, 2004). In this study, PCR technique was used to establish the identity of the causal agent of cashew anthracnose and a standardized visual key (Nathaniels, 1996) was adopted with an objective to explore the use of the relationship between incidence and severity to comparatively characterize the development of cashew anthracnose epidemics across seasons, genotypes and locations.…”

Interação enxerto e porta-enxerto na incidência da resinose do cajueiro

“…Os primeiros sintomas de resinose foram observados em quatro plantas isoladamente, em agosto de 2007, quando as mesmas atingiram a primeira safra, confirmando resultados anteriores (CARDOSO et al, 2004). Somente as plantas enxertadas com o clone CCP 76 foram afetadas nesse ano pela doença.…”

“…As plantas acometidas pela resinose têm a transpiração alterada decorrente da redução da condutância estomática e da fotossíntese líquida (BEZERRA et al, 2003). L. theobromae é capaz de colonizar tecidos de plantas sem exibir sintomas de infecção (MOHALI et al, 2005, MULLEN et al, 1991RUBINI et al, 2005), possibilitando sua disseminação através de sementes, propágulos vegetativos e porta-enxertos, de forma despercebida (CARDOSO et al, 1998;CARDOSO et al, 2004). Acredita-se que essa característica, certamente, é a maior responsável pelas epidemias observadas na microrregião do sudeste do Piauí (CARDOSO et al, 1998;CARDOSO et al, 2004;.…”