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

Abstract

Plants can resist herbivore damage through three broad mechanisms: antixenosis, antibiosis and tolerance 1 . Antixenosis is the degree to which the plant is avoided when the herbivore is able to select other plants 2 . Antibiosis is the degree to which the plant affects the fitness of the herbivore feeding on it 1 .Tolerance is the degree to which the plant can withstand or repair damage caused by the herbivore, without compromising the herbivore's growth and reproduction 1. The durability of herbivore resistance in an agricultural setting depends to a great extent on the resistance mechanism favored during crop breeding efforts 3 .We demonstrate a no-choice experiment designed to estimate the relative contributions of antibiosis and tolerance to spittlebug resistance in Brachiaria spp. Several species of African grasses of the genus Brachiaria are valuable forage and pasture plants in the Neotropics, but they can be severely challenged by several native species of spittlebugs (Hemiptera: Cercopidae) 4 .To assess their resistance to spittlebugs, plants are vegetatively-propagated by stem cuttings and allowed to grow for approximately one month, allowing the growth of superficial roots on which spittlebugs can feed. At that point, each test plant is individually challenged with six spittlebug eggs near hatching. Infestations are allowed to progress for one month before evaluating plant damage and insect survival. Scoring plant damage provides an estimate of tolerance while scoring insect survival provides an estimate of antibiosis. This protocol has facilitated our plant breeding objective to enhance spittlebug resistance in commercial brachiariagrases 5 . Video LinkThe video component of this article can be found at https://www.jove.com/video/3047/ Protocol 1. Plants 1. Single stem cuttings from mature plants are used as experimental units. The cuttings are trimmed to 10 cm to ensure uniformity of planting material. 2. To prevent contamination by plant pathogens, the cuttings are washed in a 3 % sodium hypochlorite solution for 2 min and then rinsed thoughroughly with tap water. 3. Each cutting is planted in ca. 36 g of sterile soil in a cylindrical PVC tube (5.3 cm outside diameter by 6.5 cm height) sealed at the lower end with a Styrofoam cup and capped with a PVC bushing. The cutting is held in place by a foam ring placed in the central opening of the bushing. 4. Plants are fertilized and watered as needed to maintain adequate soil moisture. 5. Plants will grow for one month before being challenged by insects, allowing development of superficial roots, which serve as feeding sites for the root-xylem-feeding spittlebug nymphs. 6. PVC tubes with rooted cuttings are inverted for 8 d prior to infestation to stimulate further the growth of superficial roots, partially adjusting for inherent differences in root architecture. This step requires an artificial source of light, which we provide for 24 h a day. To avoid confounding escapes from herbivory with herbivore resistance, individual plant replicates wit...

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Establishing Fungal Entomopathogens as Endophytes: Towards Endophytic Biological Control

“…A natural next step after refining inoculation methods, therefore, could be to examine this correlation. Several video protocols can help researchers design a suitable resistance assay for a target pest or pathogen [29][30][31] . Ultimately, it is this assay what will determine the success of the inoculation method, and the associated potential for endophytic biological control.…”

Digital imaging outperforms traditional scoring methods of spittlebug tolerance inUrochloa humidicolahybrids

“…The other five plants/genotype were not infested and used as controls. The eggs were previously obtained from the CIAT spittlebug mass rearing colony, selected for viability by visual inspection and incubated under controlled conditions (28C, 85% RH) (Parsa et al 2011). Plants were organized in a randomized complete block with two treatments (infested with A. varia and uninfested) and five replicates.…”

“…Currently, visual scoring of plant damage is the standard phenotyping method to evaluate plant tolerance to spittlebug complex in Urochloa grasses. Visual scores rely on estimates of percentages of dead leaf tissue (Parsa et al 2011). Overall, visual scoring is a low cost and medium throughput phenotyping method that has proven successful in the Urochloa breeding program of CIAT (Cardona et al 1999;Miles et al 2006).…”