Phenotyping Brachiaria Genotypes to Assess Rhizoctonia Resistance by Comparing Three Inoculum Types

Abstract

Rhizoctonia foliar blight, caused by Rhizoctonia solani, is an important disease of Brachiaria spp. in tropical America. Host-plant resistance is an attractive option for disease management. In this study, we evaluated three inoculum types (mycelium-infected agar disc, microdiscs suspensions, and microencapsulated-mycelium suspensions) in order to identify a rapid and accurate method for mass screening of Brachiaria genotypes for resistance to Rhizoctonia spp. in greenhouse trials. Visual damage score, area under the disease progress curve, and percent chlorophyll loss were estimated to determine the most accurate and precise method for evaluating Rhizoctonia resistance. The microencapsulated-mycelium solution (0.75 g/ml in potato dextrose broth sprayed on plants 30 days after planting) caused greater foliar damage than the other inoculum types and allowed effective discrimination between resistant and susceptible genotypes. The effectiveness of spray-applied, microencapsulated-mycelium was further corroborated by the evaluation of 350 genotypes not previously selected for resistance to Rhizoctonia spp., which varied significantly in their reaction to R. solani. The microencapsulated-mycelium methodology has several advantages over existing methods, including its high-throughput capacity, efficient use of time and space, ease of quantification of inoculum, and consistent results over replicate trials. This methodology could be applied to assess resistance to Rhizoctonia spp. in other crops.

Complex polyploid and hybrid species in an apomictic and sexual tropical forage grass group: genomic composition and evolution in Urochloa (Brachiaria) species

“…These activities built a global grass collection with 700 accessions of Urochloa species representing a highly diverse gene pool for breeding and systematic studies ( Keller-Grein et al , 1996 ). Valuable traits of Urochloa include biomass yield, physiological tolerance to low-fertility acid soils of the tropics ( Arroyave et al , 2011 ), digestibility and energy content ( Hanley et al , 2020 ), insect tolerance (particularly to neotropical spittlebugs; Miles et al , 2006 ) and disease resistance ( Valério et al , 1996 ; Alvarez et al , 2014 ; Hernandez et al , 2017 ). However, undesirable traits are also present, such as allelopathy (leaving bare soil; Kato-Noguchi et al , 2014 ), cold-susceptibility (hybrid Mulato II: Pizarro et al , 2013 ) and invasiveness ( Durigan et al , 2007 in the Brazilian Cerrado; Urochloa panicoides is on the US Federal Noxious Weed List https://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/weedlist.pdf ; accessed on 16 February 2021).…”

Complex polyploid and hybrid species in an apomictic and sexual tropical forage grass group: genomic composition and evolution inUrochloa(Brachiaria) species

“…These activities built a global grass collection with 700 accessions of Urochloa species representing a highly diverse gene pool for breeding and systematic studies (Keller-Grein et al ., 1996). Valuable traits of Urochloa include biomass yield, physiological tolerance to low-fertility acid soils of the tropics (Arroyave et al ., 2011), digestibility and energy content (Hanley et al ., 2020), insect tolerance (particularly to neotropical spittlebugs; Miles et al ., 2006) and disease resistance (Valério et al ., 2013; Alvarez et al ., 2014; Hernandez et al ., 2017). However, undesirable traits are also present, such as allelopathy (leaving bare soil; Kato-Noguchi et al ., 2014), cold-susceptibility (Mulato II; Pizarro et al ., 2013) and invasiveness (Durigan et al ., 2007 in the Brazilian Cerrado; U. panicoides is on the US Federal Noxious Weed List https://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/weedlist.pdf).…”

The Extent and Economic Significance of Cultivated Forage Crops in Developing Countries

“…In addition to using rangelands and native or naturalized pastures for grazing, farmers seed pastures with improved grasses and legumes and cultivate forage crops for e.g., hay, silage and fresh feed. More recently, i.e., during the last 4-5 decades, plant breeders have made important contributions to livestock productivity by developing high yielding forage varieties with tolerances to biotic and abiotic stresses (e.g., Miles et al, 2006;Miles and Hare, 2007;Aguirre et al, 2013;Cardoso et al, 2013;Rao et al, 2016;Hernandez et al, 2017;Abd El-Naby et al, 2019). Raising yields of forage crops can increase the availability and affordability of livestock products as well as reduce pressure on increasingly scarce land resources by enabling greater herd densities on existing pasture.…”