Genetic variability of drought-avoidance root traits in the mini-core germplasm collection of chickpea (Cicer arietinum L.).

Extensive and deep root systems have been recognized as one of the most important traits for improving chickpea (Cicer arietinum L.) productivity under progressively receding soil moisture conditions. However, available information on the range of variation for root traits is still limited. Genetic variability for the root traits was investigated using a cylinder culture system during two consecutive growth seasons in the mini-core germplasm collection of ICRISAT plus several wild relatives of chickpea. The largest genetic variability was observed at 35 days after sowing for root length density (RLD) (heritability, h 2 = 0.51 and 0.54) across seasons, and followed by the ratio of plant dry weight to root length density with h 2 of 0.37 and 0.50 for first and second season, respectively. The root growth of chickpea wild relatives was relatively poor compared to C. arietinum, except in case of C. reticulatum. An outstanding genotype, ICC 8261, which had the largest RLD and one of the deepest root system, was identified in chickpea mini-core germplasm collection. The accession ICC 4958 which was previously characterized as a source for drought avoidance in chickpea was confirmed as one with the most prolific and deep root system, although many superior accessions were also identified. The chickpea landraces collected from the Mediterranean and the west Asian region showed a significantly larger RLD than those from the south Asian region. In addition, the landraces originating from central Asia (former Soviet Union), characterized by arid agro-climatic conditions, also showed relatively larger RLD. As these regions are under-represented in the chickpea collection, they might be interesting areas for further germplasm exploration to identify new landraces with large RLD. The information on the genetic variability of chickpea root traits provides valuable baseline knowledge for further progress on the selection and breeding for drought avoidance root traits in chickpea

Environmental history of the dry forest biome of Guerrero, Mexico, and human impact during the last c. 2700 years

Two lake sediment cores from Madre del Sur mountain range, Guerrero State, west-central Mexico were studied to examine the past dynamics of the dry forest biome. Pollen, spores of coprophilous fungi, cyanobacteria and lithological changes are presented. The 390-cm Tixtla core (17°30′N, 99°24′W, 1400 m altitude) represents the last 2700 cal. yr; the 340-cm Huitziltepec core (17°45′N, 99°28′W, 1430 m altitude) represents the last 2050 cal. yr. Pollen shows climate-dependent competition between dry deciduous forest (with Asteraceae, Chamaesyce-type, Bursera, Euphorbia, Myrica and Lysiloma-Pithecellobium-type as main components) and moister (mesophyllous) forest (with Pinus, Quercus, Alnus and Juglans). Human impact on the environment is apparent during the entire record, as evidenced by crop cultivation (Zea mays, Amaranthus, Capsicum, Chenopodium), coprophilous fungi (Podospora-type and Sporormiella-type), deforestation (at Tixtla in particular) and lake eutrophication, ie, cyanobacteria blooms. Environmental change at both sites is summarized as follows. Period 1 (2700-2450 cal. yr BP): abundant dry deciduous forest and climate conditions drier than today. Period 2 (2450-1950 cal. yr BP): little change in proportions of dry deciduous and mesophyllous forest but floral composition of the forests differed between sites. Human occupation was low. Period 3 (1950-1550 cal. yr BP): dry deciduous forest decreased while mesophyllous forest increased, indicating more humid climatic conditions. Populations expanded significantly around 1950 cal. yr BP. Period 4 (1550-1070 cal. yr BP): maximum expansion of mesophyllous forest. Climate was more humid than today. Pre-Hispanic populations at Tixtla reached high numbers leading to deforestation and eutrophication. Period 5 (1070-c. 750 cal. yr BP): shows abundant mesophyllous forest and lowest proportions of dry deciduous forest. Climate... [ABSTRACT FROM AUTHOR

Selection in early generations to shift allele frequency for seminal root angle in wheat

A current challenge for plant breeders is the limited ability to phenotype and select for root characteristics to enhance crop productivity. The development of a high-throughput phenotyping method has recently offered new opportunities for the selection of root characteristics in breeding programs. Here, we investigated prospects for phenotypic and molecular selection for seminal root angle (SRA), a key trait associated with mature root system architecture in wheat (Triticum aestivum L.). We first investigated genetic diversity for this trait in a panel of 22 wheat lines adapted to Australian environments. The angle between the first pair of seminal roots ranged from 72 to 106°. We then evaluated selection gain via direct phenotypic selection in early generations by comparing the resulting shift in population distribution in tail populations selected for “narrow” and “wide” root angle. Overall, two rounds of selection significantly shifted the mean root angle as much as 10°. Furthermore, comparison of allele frequencies in the tail populations revealed genomic regions under selection, for which marker-assisted selection appeared to be successful. By combining efficient phenotyping and rapid generation advance, lines enriched with alleles for either narrow or wide SRA were developed within only 18 mo. These results suggest that there is a valuable source of allelic variation for SRA that can be harnessed and rapidly introgressed into elite wheat lines