An integrated approach to pest management in field pea, Pisum sativum (L.), with emphasis on pea aphid, Acyrthosiphon pisum (Harris)

[摘要] This study comprises investigations into pea aphid, Acyrthosiphon pisurn, and ascochytablight damage on field pea, the evaluation of plant resistance levels in both breeding linesand cultivars, the identification of plant resistance and the underlying mechanisms, andcultural, chemical and biological control methods. Varietal resistance studies indicated thatthere were differences between the Ethiopian and the South African strains of pea aphid withregard to their survival and reproduction on the field pea genotypes evaluated. The field peaentries performed very well against the former strain compared with the latter. Three lines(Holetta Local-90, 305PS210687 and 061K-2P-2/9/2) performed well across both strains.Field pea lines exhibiting tolerance, antixenosis and antibiosis resistance to A. pisum wereidentified under greenhouse conditions. Some lines showing high levels of antibiosis tonymphal feeding were also found in both strains. This kind of resistance mechanism maypromote insect biotype development through increased selection pressure on the pestpopulation. Strain variation was also evident in tolerance, antixenosis and antibiosisresistance. The South African strain was the least aggressive across all entries. Of the 30varietiesllines (including a local susceptible cultivar from Ethiopia) evaluated for resistanceto isolates of Mycosphearella pinodes, Oregon Sugar Pod II had a 1.9 blight severity and wasscored as resistant, three genotypes (Green Feast, Sugar Queen and line 304WAll01973)were scored as intermediate (2.1 - 3.0 severity factor) and the remaining 26 genotypes werescored as susceptible (3.1 - 4.0 severity factor) or highly susceptible (4.1 - 5.0 severityfactor). In all scoring dates, significant differences occurred among genotypes, isolates andgenotype x isolate interactions. However, the genotype x isolate interaction contribution tototal variation was much lower than that of genotypes and isolates separately. The isolate of the Denbi site in Ethiopia was slightly more virulent than those of the Holetta and Kulumsasites. Assessments regarding the potential of biological control of pea aphids using apredatory beetle (Hippodamia variegata) and entomopathogenic fungus (Beauveriabassiana) indicated that predator-treated plots supported significantly lower aphid numbersfrom the third week onwards, when compared to the fungus-treated and infested controlplots. The degree of mycosis caused by Beauveria on pea aphids was 14.3% in week threeafter inoculation and the figure dropped to 2.5% in week 5. Percentage yield loss due to peaaphid in predator-treated plots was 8.3 % compared with 16.0 % in fungus-treated plots.Field pea intercropped with Ethiopian mustard sustained less pea aphid and ascochyta blightincidence, compared to faba bean, wheat and field pea mono crop at all locations studied. Theland equivalent ratio for this particular mixed crop system exceeded 1.0, indicating that themixed crops selected were efficient for yield and monetary outcome. The increase inefficiency was ascribed to the barrier effect of mustard plants in the intercrop set-up, whichwas significant in reducing pea aphid population size and disease severity. The effect offertilizer application and sowing date on pea aphid and ascochyta blight severity was locationspecific. At the Holetta site in Ethiopia disease severity and pea aphid infestation weresignificantly reduced in fertilized plots compared with unfertilized plots, while it was onlythe disease that showed significant difference at the Denbi and Kulumsa sites. This indicatesthe importance of fertilizer application as a cultural control strategy for this disease. Neitherearly nor late sowing resulted in reduced aphid infestation and disease infection at any of thelocations. Significant interactions between variety, sowing date and fertilizer for ascochytablight was observed, indicating that the effect of one factor was influenced by the other twofactors. For aphid population density and yield, the three factors had little or no effect on each other at the Denbi and Kulumsa sites. Cultivar Markos was moderately resistant toascochyta blight and it gave higher yield compared to Mohanderfer and the varieties used byfarmers. Neem seed kernel extract application was superior to Multineem, a commercialproduct, against pea aphid development and reproduction. The neem preparationssignificantly reduced the number of molts, longevity and fecundity of A. pisum in aconcentration-dependent manner. The effect on young adults exposed to neem was not asdrastic as in the case of immatures. Acute and chronic toxicity effects on pea aphid werenoted showing that azadirachtin is an effective inhibitor of population growth of pea aphidboth on treated plants and when topically applied to the insect. Host plant resistance andnatural chemical (neem) pest control in large scale farming systems, or integrated withcultural and biological control in low-input subsistence farming systems provides effectivemanagement strategies for pea aphid and ascochyta blight in field pea. From this study,possible implementation of IPM in field pea is presented and includes aspects of varietalresistance and biological, cultural and chemical control.

[发布机构] University of the Free State