Browsing by Author "Cox, Stan"

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    Development of Perennial Grain Sorghum
    (Sustainability, 2018) Cox, Stan; Nabukalu, Pheonah; Paterson, Andrew H.; Kong, Wenqian; Nakasagga, Shakirah
    Perennial germplasm derived from crosses between Sorghum bicolor and either S. halepense or S. propinquum is being developed with the goal of preventing and reversing soil degradation in the world’s grain sorghum-growing regions. Perennial grain sorghum plants produce subterranean stems known as rhizomes that sprout to form the next season’s crop. In Kansas, breeding perennial sorghum involves crossing S. bicolor cultivars or breeding lines to S. halepense or perennial S. bicolorn × S. halepense breeding lines, selecting perennial plants from F2 or subsequent populations, crossing those plants with S. bicolor, and repeating the cycle. A retrospective field trial in Kansas showed that selection and backcrossing during 2002–2009 had improved grain yields and seed weights of breeding lines. Second-season grain yields of sorghum lines regrowing from rhizomes were similar to yields in the first season. Further selection cycles have been completed since 2009. Many rhizomatous lines that cannot survive winters in Kansas are perennial at subtropical or tropical locations in North America and Africa. Grain yield in Kansas was not correlated with rhizomatousness in either Kansas or Uganda. Genomic regions affecting rhizome growth and development have been mapped, providing new breeding tools. The S. halepense gene pool may harbor many alleles useful for improving sorghum for a broad range of traits in addition to perenniality.
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    High proportion of diploid hybrids produced by interspecific diploid 3 tetraploid Sorghum hybridization
    (Genetic Resources and Crop Evolution, 2018) Cox, Stan; Nabukalu, Pheonah; Paterson, Andrew H.; Kong, Wenqian; Auckland, Susan; Rainville, Lisa; Cox, Sheila; Wang, Shuwen
    A perennial version of grain sorghum [S. bicolor (L.) Moench] would create opportunities for greatly reducing tillage and preventing soil degradation. Efforts to select for perenniality and grain production among progeny of hybrids between S. bicolor (2n = 20) and the weedy tetraploid perennial S. halepense (L.) Pers. (2n = 40) are complicated in that F1 hybrids produced by diploid × tetraploid sorghum crosses are usually tetraploid. In 2013, a set of random pollinations between 19 diploid cytoplasmic male-sterile inbred lines and 43 tetraploid perennial plants produced 165 F1 hybrid plants, more than 75% of which had highly atypical plant, panicle, and seed phenotypes. Phenotypic segregation in F2 populations derived from atypical hybrids was also anomalous. Examination of mitotic metaphase cells in F1 or F2 root tips revealed that 129 of the 165 hybrids were diploid. Parentage of the diploid progenies was confirmed using simple-sequence repeat analysis. The mechanism by which diploid hybrids arise from diploid × tetraploid crosses is unknown, but it may involve either production of monohaploid (n = 10) pollen by the tetraploid parent or chromosome elimination during early cell divisions following formation of the triploid zygote. The ability to produce diploid germplasm segregating for S. bicolor and S. halepense alleles could have great utility, both for the development of perennial sorghum and for the improvement of conventional grain sorghum.
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    Prediction of regrowth and biomass of perennial sorghum using unoccupied aerial systems
    (Crop Science, 2022) Nakasagga, Shakirah; Adak, Alper; Murray, Seth C.; Rooney, William L.; Hoffmann, Leo; Wilde, Scott; Lindsey, Regan; Nabukalu, Pheonah; Cox, Stan
    Perennial grain sorghum [Sorghum bicolor (L.) Moench] has potential to produce grain and forage while improving soil health, ecosystem services, and carbon soil sequestration but requires further genetic improvement. Unoccupied aerial systems (UAS, also known as drones and unmanned aerial systems) provide opportunities to quickly evaluate plant traits on a large scale with precision. Unoccupied aerial system flights were used to evaluate biomass yield and rhizome characteristics of 100 diverse sorghum hybrids, most being from an interspecific hybridization program, in the establishment year and first year of regrowth. Twenty‐one vegetation indices (VIs) with canopy height measurements (CHMs) were processed from seven UAS flights made temporally during each growing season. Regression of the temporal data (VI and CHM) and phenotypic traits, including rhizome characteristics based on plant stand count (PSC), rhizome‐derived shoots (RDS), and fresh and dry biomass yields, showed useful predictions when combining temporal VI with CHM and machine learning. Blue chromatic coordinate index (BCC) best predicted all measured traits. If predictions could be generalized, UAS would reduce field evaluation time for perennial sorghum or breeding perennial grasses in general and allow breeders to evaluate additional genotypes. In this study, we found that optimizing flights to specific dates after planting could minimize resource requirements and costs in prediction of regrowth and biomass yield of perennial sorghum.
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    Rhizome development in Sorghum bicolor × Sorghum halepense families in the tropical ecosystem of Uganda
    (African Journal of Agricultural Research, 2018) Nakasagga, Shakirah; Biruma, Moses; Tusiime, Geoffrey; Nabukalu, Pheonah; Cox, Stan
    Many landraces and improved cultivars of sorghum (Sorghum bicolor) grown in Uganda have late maturity and are susceptible to several biotic and abiotic stresses. Introgression of the rhizomatous trait from perennial sorghum (Sorghum halepense) could improve stress tolerance. However, phenotypic characterization of exotic perennial sorghum germplasm under Ugandan environmental conditions is essential to select desirable genotypes. Rhizome-forming capacity of 192 S. bicolor × S. halepense backcross tetraploid families developed in a temperate North American environment was evaluated at two locations in Uganda over two consecutive growing seasons. Numbers of rhizomes and emerging shoots as well as mean distances from shoot to crown were evaluated. Forty-seven percent of families were moderately to strongly rhizomatous in the first season of growth and this value rose to 91% in the second season. Developing perennial grain sorghum for East Africa will require hybridization between exotic perennial and locally adapted germplasm. Screening for emerging rhizome-derived shoots in early generations is simple, rapid, and effective; however, more detailed selection based on both aboveground and belowground rhizome traits is recommended for later generations. Researchers and farmers should work together to find suitable ways in which perennial sorghum might fit into new types of crop and livestock systems.
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    Utilizing genetic variation in perennial sorghum to improve host plant resistance to aphids
    (Scientific Reports,, 2025) Kaler, Esha; Nabukalu, Pheonah; Murrell, Ebony; Cox, Stan; Louis, Joe
    With growing concerns over the sustainability of conventional farming systems, perennial crops offer an environmentally friendly and resilient alternative for long-term agricultural production. Perennial grain crops provide numerous benefits, such as low input investment, reduced tillage, soil conservation, better carbon sequestration, sustainable yields, and enhanced biodiversity support. Sorghum (Sorghum bicolor) is the fifth most-grown cereal crop grown for food, fuel, and food grain in the world. The development of perennial sorghum offers a substitute for traditional annual sorghum crops by providing long-term environmental, economic, and agronomic benefits. Sugarcane aphid (SCA; Melanaphis sacchari), a phloem-feeder, is considered a major threat to sorghum production. Since its first report in 2013, it caused $40.95 million in losses in South Texas alone by 2015, accounting for about 19% of the total value of sorghum production in the region. In this study, we screened diverse perennial sorghum genotypes using no-choice and choice assays to determine their innate antibiosis and antixenosis resistance levels to SCAs. Based on aphid reproduction and plant damage rating, no-choice bioassay classified the 43 perennial sorghum genotypes into four clusters: highly susceptible, moderately susceptible, moderately resistant, and highly resistant. To further investigate the resistance mechanisms, we selected two genotypes, X999 > R485 (SCA-resistant) and PR376 ~ Tift241 (SCA-susceptible) that showed the greatest variation in resistance to SCA, for subsequent experiments. Choice bioassay results indicated that aphids chose PR376 ~ Tift241 for settlement, whereas no significant preference was observed for X999 > R485 compared to the control genotype. Electrical penetration graph (EPG) results demonstrated that aphids feeding on the SCA-resistant genotype spent significantly less time in the phloem phase than the susceptible genotype and control plants. The identification of SCA-resistant perennial sorghum genotypes will be valuable for future sorghum breeding programs in managing this economically important pest.