Características morfogênicas e estruturais de cultivares diploides e tetraploides de azevém

Abstract

The annual ryegrass is a commonly used winter forage in the southern region of Brazil, due to its characteristics of production, quality and adaptability. For this extensive use, the research is being focused on improving characteristics by inducing polyploidy, that can bring gains in quality, uniformity, sugar content and leaf size. However, studies of ploidy found no differences. Thus, morphogenesis becomes an interesting tool to be used in order to distinguish groups of ploidy. The objective of this work was to evaluate morphogenic and structural characteristics of diploid and tetraploid cultivars of annual ryegrass under grazing. The experimental design was a randomized block design with three replicates. Two diploid cultivars (BRS Estações and Nibbio) and two tetraploids (Barjumbo and KLM 138) were used. The sowing was performed with density of 20 (diploids) and 25 (tetraploid) kg ha-1. Base fertilization was performed with 250 kg ha-1 of 08-02-15 and nitrogen fertilization cover of 150 kg N ha-1 applied twice. The cultivars were submitted to the "mobgrazing" grazing method, with the use of Crioula mares. The recommended heights were 25 cm and 10 cm. To evaluate the morphogenic characteristics, the "marked tiller" technique was used, and nine tillers per experimental unit were evaluated in three campaigns of six evaluations. Leaf number were measured, development and length of the blades, length of senescence, pseudoculm long and extended tiller. The data were analyzed through the SAS statistical program, and the means were compared by Student's t-test with a significance level of 5%. The highest rates of net and leaf accumulation were obtained by tetraploid cultivars. In addition, the senescence rate was also higher for these, along with the BRS Estações. It should be noted that the accumulation rate of stem is higher for Barjumbo, due to the rate of pseudoculm stretching, which possibly also contributed to the rate of total accumulation. The leaf elongation rate was also higher for the tetraploids, being the possible cause of the rates of leaf and liquid accumulation. The phyllochron, foliar appearance rate and length of elongation revealed that tetraploid cultivars presented rapid growth and tissue renewal, requiring shorter intervals between grazing. On the other hand, the diploids should be handled with larger intervals. Tetraploid cultivars also had a longer leaf length, which may lead to higher leaf production and radiation uptake, as the number of live leaves per tiller did not vary among cultivars. Also, there was no trend among groups for the population density of tillers, with diploids and KLM 138 having higher values. Also, there was a compensating effect of the leaf area per tiller, and the tetraploid cultivars obtained the lowest and the highest result.