Abstract
The cashew (Anacardium occidentale L.) crop is an important source of income for the population of the Brazilian Northeast, and anthracnose disease caused by Colletotrichum gloeosporioides leads to significant production loss. However, there is little information on either the host resistance or the variation in the aggressiveness of the pathogen under controlled environment. The reaction of commercial (CCP-06, CCP-09, CCP-76 and CCP-1001) and one non-commercial (CAP-14) dwarf cashew clones was assessed against 36 isolates of this fungus controlled environmental conditions. All the isolates, including those from hosts other than cashew, were able to cause lesions on leaves and stems of most clones, albeit to different degrees. Clone CCP-06 was the most susceptible, while clone CCP-1001 showed a level of resistance to a number of the isolates, including isolate 905, while isolates 910 and 912 were aggressive to all clones. Injury increased the susceptibility of the clones to all isolates, indicating that resistance also might be associated with structural barriers that hinder penetration. Ripened cashew apples (8-week-old), of commercial clones were susceptible to isolates 905 and 910. Immature pseudo-fruits (2-week-old), with exception of clone CCP-76 which was susceptible to both isolates showed resistance against these isolates, suggesting the presence of structural and chemical barriers. Developed nuts (8-week-old), however, were more resistant than immature nuts (2-week-old) to both isolates, probably due to their thicker exocarp cuticle and reduced number of stomatal pores.
Highlights
Until three decades ago, the production of cashew (Anacardium occidentale L.) in Brazil was based on seed propagated trees of the “Common” or “Giant” type, which lack uniformity for commercial characteristics
With the introduction of vegetatively-propagated dwarf clones of cashew, which are more uniform for agronomic characteristics (Barros and Crisóstomo, 1995), outbreaks of several diseases have become more prevalent in commercial orchards (Cardoso et al, 1999)
Clone CCP-1001 was resistant to 58% of the isolates and moderately-resistant to 22% of them, while clone CCP-06 was susceptible to 97.2% of the isolates
Summary
The production of cashew (Anacardium occidentale L.) in Brazil was based on seed propagated trees of the “Common” or “Giant” type, which lack uniformity for commercial characteristics. Such trees were grown widely-spaced in a semi-wild state and this, combined with the high level of heterozygosity in the crop, restricted the amount of disease present. With the introduction of vegetatively-propagated dwarf clones of cashew, which are more uniform for agronomic characteristics (Barros and Crisóstomo, 1995), outbreaks of several diseases have become more prevalent in commercial orchards (Cardoso et al, 1999). Any breeding programme must take into account the variation in the pathogen population
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