Itamar Cristiano Nava

Inheritance of aluminum tolerance and its effects on grain yield and grain quality in oats (Avena sativa L.)

SummaryAluminum toxicity due to the cation Al+3 is a major factor limiting yields in acid soils. Wide genetic variability to aluminum tolerance is found in oat genotypes. The objectives of this study were to determine the number of genes controlling aluminum tolerance in oats and to verify if any detrimental effects were present of the aluminum tolerance genes on grain yield and grain quality in Al+3free soils. Aluminum tolerance was estimated as the average regrowth of the main root after exposure to toxic levels of Al+3 in a hydroponic solution under controlled conditions. The number of genes controlling that trait was estimated from the distribution of the average root regrowth frequencies in a population of 333 recombinant inbred lines (RILs) in generations F5:6 and F5:7. The effects on grain yield and grain quality were assessed in a subpopulation of 162 RILs chosen based on their aluminum tolerance response. Aluminum tolerance in the evaluated population was controlled by one dominant major gene with the tolerant genotypes carying AlaAla and the sensitive ones alaala alleles. No detrimental effects of the Ala allele on grain yield or grain quality were detected.

Tiller emission and dry mass accumulation of wheat cultivars under stress

Tillers are important structures for wheat (Triticum aestivum L.) because they contribute to increase the number of spikes per area, enhancing grain yield. Stresses during plants early growth have a sizable effect on tiller production. Three experiments were conducted to evaluate the effects of stresses induced by unevenness in sowing depth, defoliation and differences in soil pH on tiller emission and dry mass accumulation of wheat cultivars. The experiments were carried out in Lages, Southern Brazil, during the winter growing seasons of 2000 and 2001. They were performed in square boxes, under natural conditions of radiation and irrigation. In the first experiment, five types of sowing depths were tested to simulate different systems of unevenness in plant emergence of cultivar Embrapa 16. In the second experiment, two wheat cultivars (BRS 177 and BRS 179) were submitted to four types of main stem defoliation. The third experiment assessed the effects of three levels of soil acidity correction on the tillering pattern of Fundacep 29. Unevenness in sowing depth, alternating pairs of seeds at 3 cm and 5 cm deep, reduced tiller emission and dry mass accumulation. The removal of the first and second main stem leaves reduced significantly BRS 179 tiller dry mass and number and did not affect the tillering pattern of BRS 177. The lack of liming restricted tiller emission and reduced plant dry mass accumulation.

ALUMINIUM TOLERANCE OF OAT CULTIVARS UNDER HYDROPONIC AND ACID SOIL CONDITIONS

Aluminium toxicity is an important abiotic factor limiting the growth and yield of oat plants ( Avena sativa L.) and other cultivated species. The objectives of this study were to evaluate the response of oat cultivars at the reproductive stage to aluminium under acid soil conditions and to compare with the responses observed at seedling stage under hydroponic conditions. In the soil, the damage to the above-ground part of the plant was estimated by the morphological response to aluminium, shoot length, shoot dry mass and plant height and, to the below-ground part of the plant as the length of roots and root dry mass. In hydroponics, the primary root regrowth was used to define the level of tolerance. The comparison of the results obtained in acid soil with those obtained in hydroponics demonstrated that both conditions produced essentially the same responses. The use of hydroponic solution can be a valuable tool for phenotyping large populations, especially useful for breeding programmes located in regions were aluminium is not present at toxic levels in the soil.

Genetics and molecular mapping of the naked grains in hexaploid oat

Avena sativa L. subsp. nudisativa has the ability to produce naked grains. Genetic studies on the naked trait of oat began over a century ago, but the genetic and molecular factors associated with the expression of this trait have not been fully clarified. The objectives of this study were to evaluate the naked trait in two oat populations of recombinant inbred lines (RILs), to determine the number of genes, to estimate the heritability, and to map genomic regions associated with the naked trait in hexaploid oat. Parental lines and RILs of each population were screened for the naked trait from plants grown in the field over a 2 year period. Based on the phenotypic data, the oat RILs were classed as naked, partially naked, partially hulled and hulled. In both populations and years, a great number of RILs showed variable expressivity for the naked trait. The genetic analysis indicated the action of a major gene (N1) with the action of modifying genes controlling the formation of naked grains. The results of the estimate of heritability show that environmental conditions do not have a great influence in determining the naked trait. The quantitative trait loci analysis detected a genomic region with a large effect on the naked trait that explained more than 50% of the phenotypic variation. Further studies are needed to validate the use of these molecular markers to assist breeding programs to select high quality and stable naked oat cultivars.

Chromosome-anchored QTL conferring aluminum tolerance in hexaploid oat

Aluminum (Al) toxicity is a major constraint on crop production in acid soils around the world. Hexaploid oat (Avena sativa L.) possesses significant Al tolerance making it a good candidate for production in these environments. Genetic improvement for Al tolerance in oat has traditionally been achieved through conventional plant breeding and could be enhanced by marker-assisted selection. The objectives of this study were to develop a chromosome-anchored genetic map for an oat recombinant inbred population and to identify SNP markers linked to quantitative trait loci (QTL) affecting root growth response to Al. Three QTL on chromosomes 7C-17A, 13A, and 19A conferring Al tolerance were identified using primary root regrowth of recombinant inbred lines derived from the cross between UFRGS 17 (Al tolerant) and UFRGS 930598-6 (Al sensitive). Localization of each QTL onto the sequenced rice genome revealed the genetic region on chromosome 13A might be associated with a putative malate transporter locus (LOC_Os06g15779). Studies of root apex tissue indicated that exudation of malate was increased in the Al-tolerant parent UFRGS17 and not in the sensitive parent. Based on these data, the malate transporter might be a candidate gene responsible for one of the Al tolerance QTL identified in this study.

Breeders' work after cultivar development: the stage of recommendation

The development of new cultivars is the ultimate goal of breeding programs and is the result of many years of hard work and dedication of breeders and their teams. An important part of the process, often neglected by geneticists, is the stage from recommendation to the production of breeder seed (post-breeding). This paper discusses the role of the breeder in the recommendation, registration, protection and marketing of new cultivars. The breeders active participation in all phases of post-breeding is fundamental to ensure that the cultivar reaches farmers quickly and can provide the benefits expected by society.