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Brachiaria grasses are sown in tropical regions around the world, especially in the Neotropics, to improve livestock production. Waterlogging is a major constraint to the productivity and persistence of Brachiaria grasses during the rainy season. While some Brachiaria cultivars are moderately tolerant to seasonal waterlogging, none of the commercial cultivars combines superior yield potential and nutritional quality with a high level of waterlogging tolerance. The Brachiaria breeding program at the International Center for Tropical Agriculture, has been using recurrent selection for the past two decades to combine forage yield with resistance to biotic and abiotic stress factors. The main objective of this study was to test the suitability of normalized difference vegetation index (NDVI) and image-based phenotyping as non-destructive approaches to identify Brachiaria hybrids tolerant to waterlogging stress under field conditions. Nineteen promising hybrid selections from the breeding program and three commercial checks were evaluated for their tolerance to waterlogging under field conditions. The waterlogging treatment was imposed by applying and maintaining water to 3 cm above soil surface. Plant performance was determined non-destructively using proximal sensing and image-based phenotyping and also destructively via harvesting for comparison. Image analysis of projected green and dead areas, NDVI and shoot biomass were positively correlated (r ≥ 0.8). Our results indicate that image analysis and NDVI can serve as non-destructive screening approaches for the identification of Brachiaria hybrids tolerant to waterlogging stress.

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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.

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Apomixis, asexual reproduction through seed, enables breeders to identify and faithfully propagate superior heterozygous genotypes by seed without the disadvantages of vegetative propagation or the expense and complexity of hybrid seed production. The availability of new tools such as genotyping by sequencing and bioinformatics pipelines for species lacking reference genomes now makes the construction of dense maps possible in apomictic species, despite complications including polyploidy, multisomic inheritance, self-incompatibility, and high levels of heterozygosity. In this study, we developed saturated linkage maps for the maternal and paternal genomes of an interspecific Brachiaria ruziziensis (R. Germ. and C. M. Evrard) × B. decumbens Stapf. F1 mapping population in order to identify markers linked to apomixis. High-resolution molecular karyotyping and comparative genomics with Setaria italica (L.) P. Beauv provided conclusive evidence for segmental allopolyploidy in B. decumbens, with strong preferential pairing of homologs across the genome and multisomic segregation relatively more common in chromosome 8. The apospory-specific genomic region (ASGR) was mapped to a region of reduced recombination on B. decumbens chromosome 5. The Pennisetum squamulatum (L.) R.Br. PsASGR-BABY BOOM-like (psASGR-BBML)-specific primer pair p779/p780 was in perfect linkage with the ASGR in the F1 mapping population and diagnostic for reproductive mode in a diversity panel of known sexual and apomict Brachiaria (Trin.) Griseb. and P. maximum Jacq. germplasm accessions and cultivars. These findings indicate that ASGR-BBML gene sequences are highly conserved across the Paniceae and add further support for the postulation of the ASGR-BBML as candidate genes for the apomictic function of parthenogenesis.

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BACKGROUND: This study aimed to 1) describe physical activity (PA) in 15 post gastric bypass surgery (GB), 16 obese (Ob), and 14 lean (L) participants (mean ± se: age = 37.1 ± 1.6, 30.8 ± 1.9, 32.7 ± 2.3 yrs.; BMI = 29.7 ± 1.2, 38.2 ± 0.8, 22.9 ± 0.5 kg/m2, respectively); and 2) test associations between PA, body composition, and cardiorespiratory fitness (VO2max). METHODS: Participants completed a PA questionnaire after wearing accelerometers from 5-7 days. Body composition was determined with DEXA and CT scans, and VO2max with open circuit spirometry. ANOVA was used to detect differences between groups, and linear regressions to evaluate associations between PA (self-reported, accelerometer), body composition, and VO2max. RESULTS: Self-reported moderate to vigorous PA (MVPA) in GB, Ob, and L participants was 497.7 ± 215.9, 988.6 ± 230.8, and 770.7 ± 249.3 min/week, respectively (P = .51); accelerometer MVPA was 185.9 ± 41.7, 132.3 ± 51.1, and 322.2 ± 51.1 min/week, respectively (P = .03); and steps/day were 6647 ± 141, 6603 ± 377, and 9591 ± 377, respectively (P = .03). Ob showed a marginally higher difference between self-report and accelerometer MVPA (P = .06). Accelerometer-MVPA and steps/day were inversely associated with percent fat (r = -0.53, -0.46), and abdominal fat (r = -0.36, -0.40), and directly associated with VO2max (r = .36). CONCLUSIONS: PA was similar between GB and Ob participants, and both were less active than L. Higher MVPA was associated with higher VO2max and lower body fat.

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Nymphs and adults of several spittlebug (Hemiptera: Cercopidae) species are key pests of forage brachiariagrasses (Brachiaria spp.) in tropical America. To support current breeding programs, a series of experiments aimed at characterizing the mechanisms of resistance to adult feeding damage were carried out. Five genotypes were used: two susceptible checks (CIAT 0606 and CIAT 0654) and three nymph-resistant genotypes (CIAT 36087, CIAT 6294, and SX01NO/0102). Test insects were Aeneolamia varia (F.), A. reducta (Lallemand), and Zulia carbonaria (Lallemand). The nymph-resistant genotypes showed tolerance to all spittlebug species tested. Tolerance in these genotypes can be classified as only moderate given the extent of losses (60-80%) caused by both female and male adults. None of the nymph-resistant genotypes had antibiotic effects on adults feeding on foliage. The results also indicated that antixenosis for feeding is not a plausible explanation for lower damage scores and less biomass losses in resistant genotypes. The fact that adult longevity (usually 8 d) was not affected when the adults were forced to feed on roots of a genotype with strong antibiotic resistance to nymphs is regarded as additional evidence that resistances to nymphs and to adults in Brachiaria are largely independent.

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Up to 50% of Brachiaria production in the tropics is affected by foliar blight caused by Rhizoctonia spp. Monothallic isolates of Rhizoctonia (n = 147) were cultured from different Brachiaria genotypes in Colombia and morphologically characterized and evaluated in pathogenicity trials in the greenhouse. Based on restriction fragment length polymorphism of the internal transcribed spacer region, 101 of the isolates were identified as Rhizoctonia solani anastomosis group (AG)-1 IA and were multinucleated, with high growth rate, brown mycelium, and high virulence; and 46 isolates were identified as Rhizoctonia sp. AG-D and were binucleated, with low growth rate, white mycelium, and lower virulence on the Brachiaria genotypes tested. The Rhizoctonia isolates also showed variation according to geographic origin, with R. solani AG-1 IA prevalent in warm lowland areas and Rhizoctonia sp. AG-D occurring in cooler areas. Ten Brachiaria genotypes were challenged with different Rhizoctonia isolates and resistant reactions were seen in three of these genotypes, including Brachiaria hybrid (International Center for Tropical Agriculture [CIAT] 36062), Brachiaria brizantha 'Marandú' (CIAT 6294), and Brachiaria hybrid 'Mulato II' (CIAT 36087). These results will contribute to a greater understanding of the interaction of diverse Rhizoctonia isolates on different Brachiaria genotypes, supporting improvement of Brachiaria spp. for disease resistance.

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Both nymphal and adult spittlebugs (Hemiptera: Cercopidae) cause serious economic damage to susceptible brachiariagrass [genus Brachiaria (Trin.) Griseb], pastures in tropical America. Both life stages are xylem feeders: nymphs feed primarily on roots and stems, whereas the adults feed mainly on foliage. Numerous interspecific brachiariagrass hybrids with high levels of antibiosis resistance to nymphs of several important spittlebug species have been obtained. Recent studies revealed major inconsistencies between reaction to nymphs and reaction to adults on the same host genotype. Because both insect life stages can cause severe economic damage on susceptible brachiariagrass pastures, a cultivar development strategy must take into account resistance to both life stages. To assess the degree of association between resistance to spittlebug nymphs and to adult feeding, we tested 164 hybrids and six check genotypes for resistance to both life stages of three spittlebug species: Aeneolamia varia (F.), Aeneolamia reducta (Lallemand), and Zulia carbonaria (Lallemand). Most hybrids tested were classified as resistant to nymphs. On the contrary, for all three species, the overall mean damage score of the 164 hybrids did not differ from the mean score of the susceptible checks. None of the hybrids was classified as resistant to adult feeding damage. Correlations between percentage nymph survival and adult damage scores were consistently low (r = 0.0104-0.0191). Correlations between nymphal and adult damage scores were also low (0.109-0.271), suggesting that resistances to the different life stages are largely independent. Chi-square analyses comparing frequency distributions of responses of the 164 breeding hybrids to nymphs or adults confirmed essential genetic independence of these two traits. We conclude that attention to improving genetic resistance specifically to adult feeding damage is warranted.

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Both nymphal and adult stages of several species of spittlebugs (Hemiptera: Cercopidae) are key economic pests of brachiariagrasses (Brachiaria spp.) in tropical America. Progress has been made in the characterization and development of antibiosis resistance to nymphs in brachiariagrasses. Essentially no attention has been given to screening germplasm for resistance to adults. To support current breeding programs, a series of experiments was conducted to develop a methodology to screen for adult damage and to study categories of resistance to adult feeding damage. Six host brachiariagrass genotypes were used: two susceptible checks (CIAT 0606 and CIAT 0654) and four nymph-resistant genotypes (CIAT 6294, CIAT 36062, CIAT 36087, and SX01NO/0102). Test insects were Aeneolamia varia (F.) and Zulia carbonaria (Lallemand). None of the nymph-resistant genotypes was antibiotic to adults. All four nymph-resistant genotypes showed tolerance to A. varia and Z. carbonaria feeding damage. The levels of tolerance to adults of Z. carbonaria, a larger, more aggressive species, were lower. Of the four nymph-resistant genotypes, only CIAT 6294 and CIAT 36087 showed some tolerance to Z. carbonaria expressed as lower leaf damage scores, less chlorophyll loss, and lower functional plant loss indices. The fact that a genotype like SX01NO/0102, which is highly antibiotic to nymphs, is susceptible to adult damage suggests that mechanisms of resistance to the two spittlebug life stages may be independent. Results of these studies suggest a need to incorporate routine screening for tolerance to adult feeding damage as an additional selection criterion in the breeding scheme.

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Several greenhouse experiments were used to measure how high levels of antibiosis resistance to nymphs in two interspecific Brachiaria (brachiariagrass) hybrids affect life history parameters of the spittlebugs Aeneolamia varia (F.) and Zulia carbonaria (Lallemand), two of the most important spittlebug (Hemiptera: Cercopidae) species affecting Brachiaria production in Colombia. The A. varia-resistant hybrid CIAT 36062, the Z. carbonaria-resistant hybrid SX01NO/0102, and the susceptible accession CIAT 0654 were used to compare the effect of all possible combinations of food sources for nymphs and adults. Calculation of growth indexes showed a significant impact of antibiosis resistance on the biology of immature stages of both species. Median survival times of adults feeding on resistant genotypes did not differ from those recorded on the susceptible genotype, suggesting that factors responsible for high mortality of nymphs in the resistant hybrids did not affect adult survival. Rearing nymphs of A. varia on CIAT 36062 and of Z. carbonaria on SX01NO/0102 had deleterious sublethal effects on the reproductive biology of resulting adult females. It is concluded that high nymphal mortality and subsequent sublethal effects of nymphal antibiosis on adults should have a major impact on the demography of the two spittlebug species studied.

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Prosapia simulans (Walker) is an important spittlebug species that attacks forage grasses of the genus Brachiaria (Trin.) Griseb. from Mexico to Colombia. This, and several other species of spittlebugs, cause important economic losses to the livestock production industry. Development of resistant cultivars is regarded as the best method of control. In the present study we used taxonomic keys, dissection of male genitalia and RAPD-PCR patterns to reconfirm the identity of P. simulans specimens collected in Colombia and Mexico. We were able to reconfirm that P. simulans occurs as a pest of Brachiaria from Mexico to Colombia. We also studied the levels and mechanisms of resistance present in 34 Brachiaria hybrids developed by CIAT. Infestations were made with six eggs per plant. We used 10 replications (plants) per genotype in a completely randomized design. Seven hybrids were found to be susceptible, 16 showed intermediate resistance and 11 were resistant. Antibiosis was the mechanism of resistance expressed in resistant hybrids as well as in the resistant checks CIAT 6294 and CIAT 36062. Tolerance was absent. The genotypes BRX 4402 and CIAT 0606 were classified as highly susceptible.

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Prosapia simulans (Walker) es una especie de salivazo que ataca los pastos del género Brachiaria (Trin.) Griseb. desde México hasta Colombia y ocasiona pérdidas económicas a la industria ganadera. El desarrollo de cultivares resistentes es considerado el mejor método de control del salivazo. Este trabajo tuvo los siguientes objetivos: corroborar la identificación de P. simulans originarias de México y Colombia, probar nuevos híbridos de Brachiaria por resistencia a esta especie y caracterizar los mecanismos de resistencia presentes en ellos. Mediante la combinación de caracteres morfológicos (uso de claves taxonómicas, disección de la genitalia del macho) y técnicas moleculares (RAPD-PCR) se logró corroborar que P. simulans es plaga de Brachiaria spp. desde México hasta Colombia. Para probar híbridos de Brachiaria y caracterizar los mecanismos de resistencia se realizó un ensayo de selección donde se sometieron 34 híbridos al ataque del salivazo. La metodología utilizada fue desarrollada en el CIAT. En el ensayo se infestó con seis huevos maduros de la especie P. simulans por planta. Se usaron diez repeticiones por genotipo en un diseño completamente al azar. En el ensayo de selección de los híbridos se detectaron siete híbridos susceptibles, 16 con resistencia intermedia y 11 resistentes. El mecanismo de resistencia que se expresó en los híbridos resistentes y en los testigos CIAT 6294 y CIAT 36062 fue el de antibiosis. BRX 4402 y CIAT 0606 fueron clasificados como muy susceptibles.

Prosapia simulans (Walker) is an important spittlebug species that attacks forage grasses of the genus Brachiaria (Trin.) Griseb. from Mexico to Colombia. This, and several other species of spittlebugs, cause important economic losses to the livestock production industry. Development of resistant cultivars is regarded as the best method of control. In the present study we used taxonomic keys, dissection of male genitalia and RAPD-PCR patterns to reconfirm the identity of P. simulans specimens collected in Colombia and Mexico. We were able to reconfirm that P. simulans occurs as a pest of Brachiaria from Mexico to Colombia. We also studied the levels and mechanisms of resistance present in 34 Brachiaria hybrids developed by CIAT. Infestations were made with six eggs per plant. We used 10 replications (plants) per genotype in a completely randomized design. Seven hybrids were found to be susceptible, 16 showed intermediate resistance and 11 were resistant. Antibiosis was the mechanism of resistance expressed in resistant hybrids as well as in the resistant checks CIAT 6294 and CIAT 36062. Tolerance was absent. The genotypes BRX 4402 and CIAT 0606 were classified as highly susceptible.

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Several genera and species of spittlebugs (Homoptera: Cercopidae) are economic pests of Brachiaria spp. grasses in tropical America. To support current breeding programs aimed at obtaining multiple spittlebug resistance, we undertook a series of studies on antibiosis and tolerance as possible mechanisms of resistance to five major spittlebug species affecting Brachiaria spp. in Colombia: Aeneolamia varia (F.), Aeneolamia reducta (Lallemand), Zulia carbonaria (Lallemand), Zulia pubescens (F.), and Mahanarva trifissa (Jacobi). Four host genotypes, well known for their reaction to A. varia attack, were used to compare their resistance to other spittlebug species: CIAT 0654 and CIAT 0606 (susceptible) and CIAT 6294 and CIAT 36062 (resistant). CIAT 0654 and CIAT 36062 were used in antibiosis studies. Tolerance studies were conducted with CIAT 0654, CIAT 6294, and CIAT 36062. Sixty-five hybrid-derived clones were used to identify levels of multiple resistance to three spittlebug species. The levels of antibiosis resistance in CIAT 36062 clearly differed by spittlebug species and were classified as follows: very high for M. trifissa, high for A. varia and A. reducta, moderate for Z. pubescens, and absent for Z. carbonaria. Our results suggest the presence of true tolerance to Z. carbonaria in CIAT 6294 and CIAT 36062, true tolerance to Z. pubescens in CIAT 6294 and a combination of tolerance and antibiosis as mechanisms of resistance to Z. pubescens in CIAT 36062. Of the 65 hybrid clones tested with A. varia, A. reducta, and Z. carbonaria, 15 combined resistance to two species and three showed antibiosis resistance to all three spittlebug species.

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