An Improved Methodology for Massive Screening of Brachiaria spp. Genotypes for Resistance to Aeneolamia varia (Homoptera: Cercopidae)

Abstract

Several species and genera of spittlebugs (Homoptera: Cercopidae) are economic pests of grasses in tropical America. They have the potential to cause serious losses on millions of hectares of improved pastures based on cultivars of several species of Brachiaria. Most of the available commercial cultivars of Brachiaria are susceptible to spittlebug. Resistance has been identiÞed in several germplasm accessions and in one of the commercial cultivars, B. brizantha (A. Rich.) Stapf ÔMarandú Õ. Brachiaria breeding projects require reliable techniques to screen for host plant resistance in large, segregating populations. A series of experiments was conducted to improve evaluation methodology. A smaller plant growth unit, supporting a single-stem, vegetative propagule, was developed and tested. Infestation levels for both adults (6 per plant) and for nymphs (10 per plant) were established. The reÞnements in screening methodology increase both reliability and capacity of the screen. Infestation of smaller plant propagules saves time, space, and physical resources. It also allows clear expression of insect damage symptoms and hence permits discrimination between tolerance and antibiosis in host plant reaction. Selection can be based on both resistance mechanisms. We outline a 2-yr Brachiaria breeding cycle which incorporates the new spittlebug resistance screening methodology.

Characterizing Herbivore Resistance Mechanisms: Spittlebugs on <em>Brachiaria</em> spp. as an Example

“…Breeding for durable resistance, therefore, requires careful consideration of what resistance mechanisms would confer most stability for a particular crop/pest system [see Kennedy et al (1987) for a comprehensive discussion on the topic] 3 . This video demonstration builds upon several previous studies designed to estimate the relative contributions of antibiosis and tolerance to spittlebug resistance in brachiariagrasses [6][7][8][9] . In contrast with choice tests or field experiments, no-choice tests ensure all plants receive the same herbivore pressure, thus providing control for differences arising from herbivore behavior (e.g., host preference, aggregation).…”

“…A few key parameters we have considered to design our test include the age of the host plants, the species and developmental stage of the spittlebugs, the infestation level, and the duration of plant-insect contact 8,9,12 . Several rounds of experimentation and protocol refinement may be needed to reach to a rapid, cost-effective, reliable, assay that adequately predicts herbivore resistance in the field.…”

Evaluation of forage grass resistance to Mahanarva fimbriolata (Stål)

“…The studies that have been conducted to select genotypes resistant to spittlebugs consider the parameters mortality and duration of the nymphal stage as the most important (Lapointe et al 1992;Cardona et al 1999). Following the criteria adopted by Lapointe et al (1992) for the nymphal stage, the grasses selected as resistant include P. maximum cv.…”

Alternative methods for rearing grass-feeding spittlebugs (Hemiptera: Cercopidae)

“…Mass-rearing is a necessary tool for evaluation of control techniques. As methodologies improve for the evaluation of fungal entomopathogens (CIAT 1999) and the screening of germplasm for host plant resistance (Cardona et al 1999), throughput is increasingly dependent on a reliable, continuous and high-level production of eggs, nymphs and adults. Streamlining the rearing methodology will help achieve these requirements as well as increase efficiency and reduce inputs of materials, labor and space.…”