ARS | Publication request: Influence of Cacao Genotypes on Soil Rhizosphere Biological Parameters Under Agro Forestry System

Submitted to: Proceedings of the International Cocoa Producer's Conference
Publication Type: Proceedings
Publication Acceptance Date: May 28, 2009
Publication Date: November 16, 2010
Citation: Arevalo-Gardini, E., Baligar, V.C., Manuel, C.S., Alegree, J.C. 2010. Influence of Cacao Genotypes on Soil Rhizosphere Biological Parameters Under Agro Forestry System. Proceedings of the International Cocoa Producer's Conference. 527-532.

Technical Abstract: Interactions of management systems and cacao genotypes have profound influence on the diversity of soil micro-fauna in the rhizosphere; and such changes may provide benefits to plant growth and development. Field experiment was established at Tarapoto, Peru during 2004 with 60 cacao genotypes in an agro forestry system of planting on moderately fertile acid Alfisols. After three years of establishment, ten cacao genotypes were selected to assess their influence on rhizosphere biological parameters (fungus and nematodes). The cacao genotypes included were three from international collection (ICS 95, UF 613, CCN 51), seven from Peru (H35, U30 from Huallaga-Ucayali collection; ICT1112, ICT1026; ICT2162, ICT2171, ICT2142 from ICT collection) and one spontaneous local hybrid was included as control. Random block design with three replications was adapted. Soil samples were collected at 0 – 20 cm of depth at the start of the study and from the rhizosphere of ten cacao genotypes during the 2007 growing season. Mycological analysis was done by serial dilution and invert plate technique to obtain different fungal genera and Barnett, Barron, Ellis and Watanabe keys were used for identification. Extraction by sieving and decantation of modified Cobb method was used for parasitic and non-parasitic nematode identification. Shannon index was used to register species richness of all the biological parameters. At the start of cacao genotypes planting soil fungus richness, population and Shannon index were 11 genera with 3.38x105 cfu gs-1 and 2.13 respectively. Three years after establishment of cacao genotypes, inter-specific differences of cacao genotypes were evident on observed biological parameters for species richness, population and Shannon Index. However, species richness and Shannon Index were lower than the initial values. Population was higher in rhizosphere of four genotypes and other genotypes had lower populations than the initial observation. At the start of the study the nematodes had richness of 13 genera with a population of 199 indiv/100ccs and Shannon index of 1.1. Inter-specify differences of cacao genotypes on nematodes were observed for species richness, population and Shannon Index. With some exceptions overall, species richness and populations were lower and Shannon Index were higher than the values observed at the start of the experiment. These results indicate that cacao genotypes had profound effects on population dynamics and species richness of the rhizosphere thereby causing an increased diversity of microfauna and microflora, which in turn could influence the growth and development of cacao.