Brachiariagrass is an important tropical forage grass cultivated around the world. Despite its global importance, the development of brachiariagrass breeding programs was delayed by the complications of recombining aposporous apomictic genotypes until the late 1980s. 'Mulato' is the first apomictic hybrid cultivar of brachiariagrass with the development of synthetic sexual tetraploid lines. An amplified fragment-length polymorphism (AFLP) linkage map of the apomictic pollen donor 'Mulato' was developed to identify molecular markers for apospory. The map contained 29 linkage groups with 272 markers. Twelve tightly clustered AFLP markers related to apospory were identified in linkage group 2. Furthermore, we identified quantitative trait loci (QTLs) for leaf width, leaf shape ratio (width/length), stem diameter and percentage of filled seeds using simple interval mapping and composite interval mapping. The AFLP markers tightly linked to apospory and QTLs associated with important agronomical traits will be valuable tools for marker-assisted selection in brachiariagrass improvement programs.

In vitro dry matter digestibility (IVDMD) is one of the most important traits for grass quality improvement. Analysis of IVDMD in laboratory with a large number of breeding populations is very laborious. The objectives of this study were to evaluate IVDMD of brachiariagrass germplasm as material in breeding program, and also to determine the appropriate selection criteria for high digestibility. IVDMD (pepsin‐cellulase method), morphology traits and water content of 17 genotypes of Brachiaria spp. (B. brizantha, B. decumbens, B. ruziziensis and Brachiaria hybrid) were evaluated at two harvesting times, winter and early summer seasons. The correlations among traits were determined, and their heritability were also estimated. IVDMD ranged from 48.9 to 59.0% in winter, and 42.9 to 54.4% in early summer. Among morphological traits, leaf‐stem index (ratio of leaf width/stem diameter) showed the highest correlation with whole plant IVDMD (r = 0.74) followed by leaf‐shape ratio (leaf width/leaf length; r = 0.72), and leaf water content also highly correlated with whole plant IVDMD (r = 0.79). The broad sense heritability of IVDMD and the related traits of two harvests combination were high with the range of 0.75–0.93. The results demonstrate that leaf‐stem index, leaf‐shape ratio and water content could be the useful selection criteria for the breeding of brachiariagrass for high digestibility.

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A greenhouse pot-experiment was conducted to evaluate the phytoremediation abilities of three tropical pasture grasses (signalgrass, napiergrass and atratum) in response to two types of soils (Kunigami-maji and Shimajiri-maji) contaminated with three levels of lead (0, 150 and 300 mg kg -1 ). The results demonstrated that the dry biomass, lead concentration and the accumulated amounts were different among the plant species and between the soil types. The amounts of dry matter in three tropical pasture grasses grown on Kunigamimaji soil were higher than that on Shimajiri-maji soil. On both soils, lead concentration of roots was higher than that of shoots, and it was suggested that transportation of lead from roots to shoots was restricted in these plants. The lead accumulated amounts per plant grown on Kunigami-maji soil were higher than that on Shimajiri-maji soil. And, on Kunigami-maji soil, accumulation of lead was relatively high in both shoots and roots of signalgrass and atratum, while, in napiergrass, the high level of lead was found only in roots. Amounts of lead extracted from the shoots of signalgrass, napiergrass and atratum grown on Kunigami-maji soil contaminated with the highest lead level of 300 mg kg -1 were 1.64, 0.17 and 0.92 mg plant -1 , respectively. As Kunigami-maji had lower soil pH than Shimajiri-maji, it can be suggested that lower soil pH may enhance lead bioavailability and uptake by the tropical pasture grasses. In conclusion, signalgrass and atratum could be useful for phytoremediation of lead contaminated soil, especially on Kunigami-maji soil.

Liming the contaminated soil is the most widely used remediation treatment to reduce the bioavailability of heavy metals. The objective of this study was to evaluate the effect of liming on the change of dry matter and lead uptake by three tropical pasture grasses from lead contaminated acidic soil. Lime at five rates of 0, 1, 2, 3 and 4 g kg−1 soil was amended to the Neubauer's pots filled with 500 g Kunigami‐maji soils and then the limed soil was contaminated with 150 mg kg−1 lead after it was maintained for 1 week. Addition of lime increased soil pH significantly from 4.43 to 5.40. The root and shoot dry matter of all three tropical pasture grasses increased with the increasing doses of lime. An elevation of soil pH induced by liming resulted in a significant reduction of lead concentrations in both roots and shoots of all experimental grasses. The effectiveness of liming on lead concentration and accumulation varied with the pH values of limed soil and grass species. The results of this study imply that napiergrass was the most effective tropical pasture grass in reducing lead concentration and accumulation of roots and shoots as a consequence of liming, and could be used for lead stabilization in moderately lead contaminated acidic soil. The shoot lead concentration of napiergrass in limed soils was within the critical level of lead tolerable to feeding domestic animals, and may act as low level lead toxicity in fodder for grazing livestock. However, lime application or soil pH had a little influence on the lead accumulated amount in roots and shoots of atratum and signalgrass. The high amounts of lead accumulated in shoots of atratum and signalgrass were found to be useful for lead phytoextraction.

Two field trials were conducted in Thailand to determine an appropriate closing cut date (CCD) and rate of nitrogen application (N-rate) to maximize seed yield and seed quality of the two novel cultivars (cv.) of Urochloa spp. (Synonym Brachiaria spp.), cv. ‘OKI-1’ (an open-pollinated tetraploid Urochloa ruziziensis (R. Germ. and C.M. Evrard) Crins originated from cv. ‘Miyaokikoku-ichigou’) and cv. ‘Br-203’ (U. ruziziensis cv. ‘Miyaokikoku-ichigou’ × U. hybrid cv. ‘Mulato’). The following treatments were evaluated in this study: four CCDs (uncut, 15 June, 1 July, and 15 July) and four N-rates (0, 50, 100, and 150 kg/ha). The cv. ‘OKI-1’ showed somewhat differences in tiller number/m2 (TN), fertile tiller percentage (FTP), inflorescence number/tiller (IN/T) and spikelet number/raceme (SN/R) with the CCD, while the cv. ‘Br-203’ showed only in SN/R. However, TN and SN/R were highest for 15 June, and FTP and IN/T were highest for 1 July in cv. ‘OKI-1’. The cv. ‘OKI-1’ showed the highest total seed yield (TSY), pure seed yield (PSY), and pure germinated seed yield (PGSY) for 1 July, followed by 15 June, and the cv. ‘Br-203’ showed the highest TSY, PSY, and PGSY for 15 July, followed by 1 July. Nitrogen (N) fertilization showed a negative effect on TSY for both the cultivars due to the higher N content in the soil. Withholding N fertilizer, a CCD in late-June to early-July and early-July to mid-July is recommended for cv. ‘OKI-1’ and cv. ‘Br-203’, respectively.

Urochloa (syn. Brachiaria) cultivars are widely used as forage for ruminants in tropical countries and also in Thailand. Two new Urochloa cultivars, OKI-1 and Br-203, have high forage yield and digestibility compared with other cultivated Urochloa grasses. Seed production is a fundamental requirement for widespread sowing, and it can be increased by optimizing agronomic practices, such as changing plant spacing. Two field trials were conducted in 2018-2020 at Lampang Animal Nutrition Research and Development Center, Northern Thailand, to determine the optimal plant spacing for seed production of these Urochloa cultivars. In both trials, four plant-spacing regimes (50 Â 100, 75 Â 100, 100 Â 100 and 125 Â 100 cm) were used in a randomized complete block design with four replicates. In two consecutive harvests of both trials, plant spacing did not significantly affect seed yield and quality but affected tiller and inflorescence densities. Specifically, significant higher numbers of tillers and inflorescences were produced per unit area at the narrowest plant spacing (i.e., 50 Â 100 cm). OKI-1 and Br-203 tended to have higher pure seed yields (PSY) at plant spacings of 100 Â 100 (136.46 kg/ha) and 75 Â 100 cm (79.59 kg/ha), respectively. Both cultivars showed similar trends in PSY, filled seed percentage and a thousand seed weight, which tended to be higher in the first-year crops than the secondyear crops. This difference could be attributed to a reduction in available soil N resulting from a large amount of N utilization during vegetative growth, combined with inadequate and erratic rainfall. In addition to the recommended optimum plant spacing, sufficient fertilizer and suitable environmental factors could increase seed yield.