Temperate/Tropical Transition Zones: A Hotspot for Breeding Forages with Climate Resiliency

Species resiliency to climate change is critical for sustainability of grassland agricultural systems. Transition zones between temperate and tropical climates (between 27 and 31° N and S latitude) with variable annual frost/freeze events have proven to be ideal zones for identification of species with variable climate adaptation. This paper will identify these regions around the globe and show how these regions offer distinct advantages in terms of selection for abiotic and biotic stresses, and thus resiliency to changing climate. Programs located in these regions have the advantage of exposure to alternating extreme warm and cold temperatures, drought and flood conditions, and a multitude of biotic stresses. Examples are presented of successes and constraints in moving cool season species into warmer climates, and tropical species into cooler climates. We present rationale for which direction of species movement (tropical to temperate vs. temperate to tropical) may be more likely to encounter success and why. Specific plant attributes that contribute to climate resiliency will be identified and described. The ability to identify small changes in genetic photoperiod responses in these regions, where daily changes are less than 1.5 m, are illustrated as a further advantage when the objective is development of earlier or later maturity. These regions also provide suitable environments for pests, from both tropical and temperate areas, including diseases, nematodes, and insects, providing desirable field environments for screening and genetic improvement through cycles of recurrent selection. A discussion of reproduction method is included to illustrate the need to accomplish seed production of these species in other zones in order to produce higher yields of high-quality seed

Screening and Breeding for Bermudagrass Stem Maggot (BSM) Resistance Using U.S. Bermudagrass Germplasm

Bermudagrass (Cynodon sp.) is an important perennial forage grass grown in many parts of the world. Bermudagrass Stem Maggot (BSM) (Atherigona reversura Villeneuve) is an insect pest that reduces forage yield and nutritive value if it is not controlled. The pest, native to SE Asia, was first documented in North America in 2009 and is now considered invasive. A collection of over 300 forage bermudagrass accessions was evaluated in the field for susceptibility to BSM in 2014 and 2015. Tolerant lines and susceptible checks were then evaluated for yield loss due to BSM in a replicated field study by comparing insecticide-sprayed plots to unsprayed plots in Tifton, GA starting in 2016 continuing through the summer of 2019. For mid to late summer harvests during 2017, BSM reduced yield of Alicia and Russell by over 40% and Tifton 85 by up to 35%. However, tolerant accessions exhibited less than 10% yield loss and had dry matter yields comparable to Tifton 85. Nutritive value will also be assessed. These accessions will be further evaluated and used in plant breeding

Moving Warm-Season Forage Bermudagrass (\u3ci\u3eCynodon\u3c/i\u3e sp.) into Temperate Regions of North America

Warm-season (C4) perennial grasses are grown over millions of hectares in the Southeastern United States. These grasses produce optimal growth at 30 to 38°C diurnal temperature. Bermudagrass (Cynodon sp.) has been adopted as the preferred forage for many livestock and hay producers. Compared to other native and introduced warm-season perennial grass species, improved bermudagrass varieties produce high biomass with enhanced digestibility for ruminant grazing or feed. Until the 1930’s pastures in the region consisted of unimproved ‘common’ bermudagrass (Cynodon dactylon (L.) Pers.) that had been introduced earlier. However, in the early 20th century, new germplasm, including stargrass (C nlemfuënsis Vanderyst) was collected, primarily from Africa. This germplasm provided a source for major improvements in yield and digestibility. Unfortunately, stargrass is not cold tolerant, limiting it to regions between 30°N and 30°S. Intercrossing of C. nlemfuënsis with C. dactylon has produced highly successful cultivars, such as Tifton 85, which can survive at northern latitudes of at least 35°. However, there has been a desire to extend adaptation further north into the warm-season/cool-season grass transition zone. This would require a combination of breeding to improve cold tolerance in clonally-propagated varieties and development of seeded varieties that could be re-seeded following extremely cold winters. Earlier work at Oklahoma State University indicated that some cultivars had significantly different tolerance to freeze. Screening the Tifton, GA, USA core collection of 175 accessions in a northern, high-altitude location, has identified germplasm with promising cold tolerance. A breeding line (Tifton 79-16) had significantly higher yields at the northern Georgia location than the cold tolerant cultivar (Tifton 44). A number of plant introductions had higher yields as well

Seasonal Expression of Apospory in Bahiagrass

Flowering plants can reproduce sexually (outcrossing and/or selfing) and/or asexually. Sexual reproduction implies the successful completion of meiosis and double fertilisation for the formation of both the embryo and the endosperm. In contrast, gametophytic apomixis is an asexual mode of reproduction through seeds that involves parthenogenetic embryo development from a cytologically unreduced egg cell (2n). Apospory is the process by which unreduced gametophytes are formed after a series of mitotic divisions of somatic cells (2n) in the ovary. This occurs independently from the sexual meiotic process; and therefore, both sexual and apomictic pathways may coexist simultaneously. Apospory is inherited in bahiagrass (Paspalum notatum) as a single dominant Mendelian factor with distorted segregation (Martínez et al. 2001), and its degree of expression was reported to vary throughout the flowering season in P. cromyorrhizon, a close relative of bahiagrass (Quarin 1986). Bahiagrass is a perennial warm-season grass widely used for forage and utility turf in the south-eastern US due to its persistence in sandy, infertile soils. Diploid races reproduce sexually and are highly self-incompatible (Acuña et al. 2007), while polyploids are classified as pseudogamous apomicts (pollination is required) (Quarin 1999). Sexual tetraploid genotypes have been experimentally created (Quesenberry and Smith 2003; Quesenberry et al. 2010) and successfully used in crosses (Acuña et al. 2009). Cytoembryological analysis has been used to determine the mode of reproduction in bahiagrass (Martínez et al. 2001; Acuña et al. 2007). At anthesis, sexual plants produce spikelets having only a single Polygonum type meiotic embryo sac (SES), characterised by bearing the egg apparatus close to the micropyla, a large binucleated central cell and a group of antipodal cells at the chalazal end (Figure 1a). Highly apomictic plants produce ovules having single or multiple aposporous embryo sacs (AES), which present the egg apparatus and a central cell with 2 polar nuclei, and no antipodal cells (Figure 1b). Some tetraploid bahiagrass races are also able to produce ovules that have the sexual meiotic megasporocyte together with one or more aposporous sacs (AES+SES), and these plants are classified as facultative apomictic. The objective of this study was to characterise the reproductive mode of 5 wild dwarf bahiagrasses, a highly apomictic hybrid (Acuña et al. 2009) and the cultivar ‘Argentine’ at different times during the flowering season and under different nitrogen (N) fertiliser rates

Natural genetic diversity of nutritive value traits in the genus Cynodon

The Cynodon spp. collection maintained by United States Department of Agriculture National Plant Germplasm System (USDA-NPGS) has limited information on nutritive value (NV) traits. In this study, crude protein (CP), phosphorous concentration (P), in vitro digestible organic matter (IVDOM), and neutral detergent fiber (NDF) were determined to (i) estimate genetic parameters for NV, (ii) obtain genetic values for the whole population across two harvests, (iii) estimate genotype by harvest interaction (GHI) for NV traits, and (iv) select accessions exhibiting improved NV traits compared to ‘Tifton 850 . The experiment was setup as a row-column design with two replicates and augmented representation of controls: Tifton 85, ‘Jiggs’, and ‘Coastal’. The whole-population was harvested twice, and data were analyzed using linear mixed models with repeated measures. In addition, a selected population of 15 genotypes were evaluated across 11 harvests to determine the extent of GHI. Genetic parameters revealed the presence of significant genetic variability, indicating potential improvements for NV through breeding. Specifically, P and IVDOM presented large variation, while NDF had lower diversity but some accessions exhibited lower NDF than Tifton 85. Low GHI, except for IVDOM, indicated genotypic stability and potential for selecting improved accessions under fewer harvests. Breeding line 240, PI-316510, and PI-3166536 presented superior NV than Tifton 85

Plant Breeding Perspectives for Alfalfa (\u3cem\u3eMedicago sativa\u3c/em\u3e L.) Success in Warm Climates

Climate change can have major impacts on adaptation of forage species to agroecosystems around the world. The ability of breeders to select for traits that impart adaptability to climate resilience will be critical for the future of grasslands. Alfalfa (Medicago sativa L.) is the most important perennial forage legume in the world because of its relatively high yield and nutritional value. In Florida, nondormant cultivars were developed for improved adaptation to the state’s subtropical agroecosystem (‘Florida 66’, ‘Florida 77’, and ‘Florida 99’); however, these cultivars are not commercially available. Breeding efforts are underway to develop new nondormant alfalfa adapted to subtropical conditions. The main goal of the alfalfa breeding program at the University of Florida (UF) is to combine germplasm screening, genomics, enviromics, and phenomics to improve yield and persistence. The integration of multi-omics data can result in greater genetic gain by reducing the length of the breeding cycle and by increasing the size of breeding populations. The development of nondormant, persistent, and high yielding cultivars would be a big step towards establishing alfalfa systems in warmer climates

Annual Clovers Around the World: Current Status and Future Prospects

This paper reviews the distribution and importance of annual clover (Trifolium) species for pasture and fodder production systems globally. Of the 158 recorded annual Trifolium species, 65.2% are endemic to the Mediterranean basin and surrounding areas, 14.6% to sub-Saharan Africa, 17.7% to the United States of America and 2.5% to Chile. Fourteen species have been commercialised, while other endemic and naturalised annual clovers are also utilised. Key species for self-regenerating pastures include T. subterraneum, T. michelianum and T. respinatum var. resupinatum, while major dual-purpose grazing and fodder species include T. incarnatum, T. vesiculosum, T. alexandrinum and T. respinatum var. majus. Less important commercial species include T. hirtum, T. squarrosum, T. nigrescens and T. cherleri. Australian scientists have also recently domesticated T. glanduliferum, T. spumosum, T. purpureum and T. dasyurum. The areas sown to annual clovers may increase in future years, due to increasing nitrogen (N) fertiliser costs, environmental concerns with N runoff. Climate change brings new challenges and opportunities for annual clovers. The forage plant genetic resource centres will be crucial for developing new adapted cultivars

Agronomic performance of interspecific Paspalum hybrids under nitrogen fertilization or mixed with legumes

Nitrogen supply and mixtures with legumes affect agronomic performance of pas- tures, and both practices can guide breeding decisions in Paspalum hybrids. The goals of this study were: (a) quantify herbage accumulation (HA), leaf accumulation (LA), cold tolerance, and N use efficiency (NUE) in P. plicatulum × P. guenoarum hybrids subjected to N fertilization or grown in a mixture with legumes; (b) compare the grass–legume system to a grass–N fertilizer system; and (c) select the best hybrid for future cultivar releases. A randomized complete block design with three repli- cations and a split-plot treatment arrangement was used for 2 yr, with five N rates (0, 60, 120, 240, and 480 kg N ha−1) and a grass–legume mixture [grass + white clover (Trifolium repens L.) + birdsfoot trefoil (Lotus corniculatus L.)] as whole plots, and six genotypes as subplots (hybrids: 1020133, 102069, 103084, 103061; and controls: P. guenoarum ‘Azulão’ and Megathyrsus maximus ‘Aruana’). Higher N rates increased HA, LA, and cold tolerance. Higher NUE was obtained between 60 and 120 kg N ha−1. In the grass–legume mixture HA was similar to the rates of 60 and 120 kg N ha−1. Hybrid 1020133 had HA similar to the controls, LA greater than Aruana, and greater cold tolerance and NUE at 60 kg N ha−1 than Azulão and Aruana. Hybrid 1020133 should be selected for further animal performance stud- ies. The agronomic performance of perennial pastures can be improved through N management, and NUE should be a selection criterion in forage breeding

Sorghum [Sorghum bicolor (L.) Moench] and cowpea [Vigna unguiculata (L.) Walpers] intercropping improves grain yield, fodder biomass, and nutritive value

Burkina Faso livestock feeding is characterized by a hot dry season fodder deficit, which affects animal performance and causes economic losses. To overcome this challenge, improving quality fodder production through the use of dual-purpose crops is a potential alternative. Hence, this study aimed at testing dual-purpose cultivars of sorghum and cowpea under monoculture and intercropping in the North Sudan zone in Burkina Faso. To do this, a “Mother and Baby trials” approach was adopted. The mother trial was designed as a randomized complete block with eight treatments (combinations of monoculture and intercropping systems for two cowpeas and two sorghum cultivars) and four replications during two cropping seasons (2019 and 2020) at the INERA research station in Saria. The on-farm “baby” trials involved 30 farmers during two cropping seasons (2019 and 2020) in four communes: Koudougou, Poa, Nandiala, and Kokologo. Data were collected on weed biomass and density, fodder biomass and grain yield, intercropping efficiency, and fodder nutritive value. The results of the mother trial showed that intercropping significantly (p ≤ 0.05) reduced weed density and weed biomass. Sorghum cultivar Ponta Negra had the highest fodder biomass yield (10.05 kg DM/ha) while sorghum Sariaso16 had the highest grain yield (4.42 kg/ha). Cowpea cultivar KVx745-11P had greater fodder biomass (4.72 kg DM/ha) than Tiligré (3.28 kg DM/ha) with similar grain yield (2.17 and 2.17 kg/ha). Intercropping was the most efficient land-use cropping system for fodder biomass and grain yield improvement both in mother and baby trials. For fodder nutritive value, cultivars Sariaso16 and Ponta Negra had similar crude protein concentrations (ranging from 4.1 to 5.4%), and cowpea cultivar KVx745-11P haulms had greater crude protein (ranging from 16.9 to 20.3%). The use of Ponta Negra and KVx745-11P and Sariaso16 and KVx745-11P under intercropping is likely to optimize grain and quality fodder production for crop-livestock farmers in the North Sudan zone