The Effect of Inflorescence Density of Grain Amaranth (Amaranthus spp) on Cletus fuscescens (Walker) (Hemiptera: Coreidae) Infestation

Study Design: Field experiments were laid out in a randomized complete block design while the laboratory experiments were laid out in a completely randomized design.
Place and Duration of Study: Experiments were conducted at the vegetable field and entomology laboratory of the National Horticultural Research Institute, Ibadan, Nigeria, during the rainy seasons of 2009 and 2010.
Methodology: Nine accessions of grain amaranth comprising of 3 accessions with lax inflorescence (RRC 646, P 373 and Oscar Blanco), 3 accessions with intermediate inflorescence (RRC 1027, Tibet and Niqua) and 3 accessions with dense inflorescence (D70-1, RRC 551 and Zhen Ping) were planted in the field. Weekly visual counts of C. fuscescens adults and nymphs on six middle plants randomly selected and tagged per plot were made in the morning, a week after transplanting through grain maturity. At grain maturity the inflorescence morphological characters, inflorescence color, inflorescence density index, inflorescence shape were rated. Seed viability test of the harvested grain was conducted in the entomology laboratory.
Result: Accessions with intermediate inflorescence had highest C. fuscescens populations/ plant and least viability percentage implying susceptibility to C. fuscescens attack while accessions with dense inflorescence had lowest C. fuscescens populations/ plant and highest seed viability percentage (P=.05) due to compactness of the inflorescence which inhibited feeding by the insect, exhibiting an antixenosis resistance. C. fuscescens populations/ plant correlated negatively with only seed viability percentage (P=.05). Also stepwise regression analysis selected viability percentage as the most important variable reflecting C. fuscescens infestation (P=.05).
Conclusion: Dense inflorescence in amaranth accessions could be a source for conferment of antixenosis resistance to C. fuscescens attack while high yielding intermediate inflorescence density index though susceptible to C. fuscescens attack could be utilized for yield improvement in breeding programme.