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Development of Selection and Clonal Propagation techniques for Multiplication of Elite Yield and Anthracnose Tolerant Cashew (Anacardium occidentale L.)

Objective

- To identify elite yield and anthracnose-tolerant cashew trees in wild and domesticated stands to be clonal propagated or to be used as "plus" trees in further breeding programmes;
- To introduce elite yield and anthracnose-tolerant germplasm into Brazil, Guinea-Bissau and Morocco;
- To strengthen research and training links between Moroccan, West African and European countries with Brazilian centres where traditional approaches to cashew breeding and selection have been underway in the natural genetic diversity of the Anacardium genus;
- To strengthen research and training links between Morocco, Guinea-Bissau and Brazil with European countries where new approaches like cashew in vitro propagation and biochemical and molecular fingerprint characterisation are being carried out.
Field work
- The Portuguese and Moroccan partners visited at different times, with the Brazilian team, the North East of Brazil where the origin centre of cashew species is located. During these missions the biodiversity of cashew and other Anacardium sp. in native and semi-spontaneous conditions was detected and seed was collected to improve germplasm collections. The characteristics of the improved dwarf clones were registered. Clones from this material were planted at UFAL and seed was collected for research experiments. During these missions the partners recognised the Brazilian experience on cashew growing, cashew breeding and by products technology. Being part of the project the introduction of this crop in Morocco, improved cashew genotypes from Brazil and from selected trees in Guinea-Bissau were introduced to test their adaptation to the Moroccan conditions. In Guinea-Bissau 4 progeny fields were established in different edapho-climatic regions with progenies of 34 cashew plants locally selected and 6 introduced genotypes. These fields are being followed and comparative observations will be carried out during the next years.
Cashew Vegetative Propagation
- Different in vitro approaches have been developed to establish a clonal propagation technique for cashew true-to-type multiplication. Different factors are being studied for the apical and axilary node culture. The effect of different media (growth regulators, gelling agents, carbon sources, activated charcoal, salts, vitamins) and of in vitro conditions (light, temperature) are being studied to optimise the induction of bud break, flush growth and flush elongation. Comparative studies have been carried out for rooting induction such as kind and concentration of auxin (IBA and IAA) and duration of the treatment. Adventitious rooting has been successfully obtained in different organs such as shoots, cotyledons and leaf pieces. Rooted plantlets were successfully weaned (100%). Results on cashew micrografting showed that this technique is reproductible and that the survival score reached the 80%. In vitro seedlings have been used as rootstocks that have been grafted with buds from in vitro or glasshouse-raised plants. Other approaches for cashew propagation such as somatic embryogenesis are being carried out.

Anthracnose Studies
- Two collections of Colletotrichum gloeosporioides isolates collected from cashew and other fruit trees in several places of North-East Brazil and Guinea-Bissau were established in Brazil and Portugal. The isolates were characterised according to their cultural aspect, growth rate and sporulation in potato dextrose agar (PDA), malt extract agar (MEA), oatmeal dextrose agar (ODA) and oatmeal yeast extract agar (OYA) at the temperatures of 15, 20, 25, 30 and 35ºC. The best medium for the fungus growth was PDA whereas for sporulation it was OYA. The growth at several temperatures in MEA pointed out to interactions between the isolates studied and the temperatures with a growth optimum among 25 and 30ºC. Most of the isolates showed good germination in vitro at the referred temperatures. Few isolate did germinate at 38ºC although without appressoria formation. Pathogenicity tests were carried out on detached young leaves by inoculations with 4mm discs containing mycelium of the fungus isolate. Some isolates were more virulent than others in terms of the number of genotypes showing susceptibility to them. Two isolates of the several tested on pistachio behaved as virulent to this species. These studies with C. gloeosporioides from cashew give evidence, for the first time, about the variability among the fungus isolates and cashew genotypes.
* To select elite dwarf and giant anthracnose-tolerant cashew trees in wild and domesticated stands of the North East of Brazil and Guinea-Bissau and to genetically characterise them by biochemical and molecular methods;
* To characterise the pathogenicity of Collethotrichum sp. isolates obtained from wild and domesticated cashew trees of the North East of Brazil and Guinea-Bissau;
* To increase basic understanding of natural growth in cashew by using biochemical and molecular approaches;
* To develop by in vitro and conventional propagation techniques, elite yield and anthracnose-tolerant germplasm in order to introduce it into Brazil, Guinea-Bissau and Morocco.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Instituto de Investigação Científica Tropical
Address
86,Tapada De Ajuda
1300 Lisboa
Portugal

Participants (4)

Institut Agronomique et Vétérinaire Hassan II
Morocco
Address

10100 Rabat
Ministerio do D. Rural e Agricultura
Guinea-Bissau
Address

Bissau
Universidade Federal de Alagos
Brazil
Address
Cidade Universitaria - Tabuleiro
Maceio - Al
Wye College
United Kingdom
Address
Wye
TN25 5AH Ashford