Massimo Saccomani

A comparison of root characteristics in relation to nutrient and water stress in two maize hybrids

Root responses of maize (Zea mays L.) to limited nutrients and water availability were evaluated in two highly productive full-season hybrids, DK585 and Santos (Dekalb — Monsanto), in laboratory, pot and field tests. In the laboratory, under optimal nutrient and water supply, seedlings of DK585 had higher growth (leaves and roots). Under nitrate or sulphate deprivation, DK585 showed better ability in adapting its root/shoot ratio to stress conditions, whereas Santos showed less plastic behaviour. This morphological trait of DK585 was associated with higher sulphate and constitutive nitrate influxes. In pot trials (plants with four to five leaves), DK585 maintained a high transpiration level to very low values (around 0.2) of FTSW (fraction of transpirable soil water), whereas Santos showed a higher response to soil drying. The latter reduced the rate of transpiration starting from a FTSW of about 0.6. In the open field (trial in 2000, Legnaro, NE Italy), in conditions of fluctuating combined water and nitrogen stress, DK585 at flowering reached greater root length density (RLD) than Santos in deep layers (50–100-cm interval depth) of positions further from the plant. However, in these conditions, the yield of DK585 was found to be only slightly higher than that of Santos (8.88 vs. 8.49 t ha.−1 d.w.). An overall evaluation of the two hybrids indicates the more conservative strategy towards limited water and nutrient resources in Santos, and a greater tendency towards stress avoidance in DK585.

Effect of nitrogen and/or sulfur deprivation on the uptake and assimilation steps of nitrate and sulfate in maize seedlings

Abstract Seedlings of two maize genotypes, differing in grain yield, were deprived for five days of either nitrogen or sulfur, or both. At the end of each shortage period, prior to the development of any deficiency symptom, uptake rates and internal pools of sulfate and nitrate, extractable activities of ATPS, OASS, NR, GDH, GS were evaluated. The comparison with seedlings supplied with complete solution showed that after S + N deprivation the rate of sulfate uptake was enhanced 46 and 30% in the higher and lower yield genotype respectively, while that of nitrate was the same of control. In both genotypes GS activity did not change, sulfate and nitrate internal pools were reduced and significant changes in activity concerned NR, which was strongly depressed, GDH, which increased 35%. OASS increased 60 and 30% in the higher and lower yield genotype respectively. In the case of deprivation of only one of the two elements, each of the metabolic parameters tested, except GS activity, was differently affected ...

Genome-enabled predictions for binomial traits in sugar beet populations

BackgroundGenomic information can be used to predict not only continuous but also categorical (e.g. binomial) traits. Several traits of interest in human medicine and agriculture present a discrete distribution of phenotypes (e.g. disease status). Root vigor in sugar beet (B. vulgaris) is an example of binomial trait of agronomic importance. In this paper, a panel of 192 SNPs (single nucleotide polymorphisms) was used to genotype 124 sugar beet individual plants from 18 lines, and to classify them as showing “high” or “low” root vigor.ResultsA threshold model was used to fit the relationship between binomial root vigor and SNP genotypes, through the matrix of genomic relationships between individuals in a genomic BLUP (G-BLUP) approach. From a 5-fold cross-validation scheme, 500 testing subsets were generated. The estimated average cross-validation error rate was 0.000731 (0.073%). Only 9 out of 12326 test observations (500 replicates for an average test set size of 24.65) were misclassified.ConclusionsThe estimated prediction accuracy was quite high. Such accurate predictions may be related to the high estimated heritability for root vigor (0.783) and to the few genes with large effect underlying the trait. Despite the sparse SNP panel, there was sufficient within-scaffold LD where SNPs with large effect on root vigor were located to allow for genome-enabled predictions to work.

Evaluation of genetic diversity and root traits of sea beet accessions of the Adriatic Sea coast

Thirty-nine sea beet [Beta vulgaris L. ssp. maritima (L.) Arcang.] accessions of the Adriatic coast were screened genetically and for their adaptive morpho-functional root traits in order to identify new sources of abiotic resistances for sugar beet breeding programs. Genetic diversity was evaluated with 21 microsatellites markers that identified 44 polymorphic alleles. Sea beets grouped into two main clusters: the West and the East Adriatic coast groups, with the latter showing higher genetic diversity. Among sea beet accessions with desirable root traits, four accessions have proved to be interesting for sugar beet [B. vulgaris (L.) ssp. vulgaris] breeding aimed to improve tolerance to nutritional stresses. Lastovo (ID 29) and Zut (ID 34) accessions were characterized by the highest values of RER, TRL, FRL and RSA still maintaining a high value of RTD, while Grado (ID 21) an Portic (ID 23) accessions were characterized by the highest RTD, but with low values of RER, TRL, FRL and RSA parameters.

Identification and Validation of a SNP Marker Linked to the Gene HsBvm-1 for Nematode Resistance in Sugar Beet

The beet-cyst nematode (Heterodera schachtii Schmidt) is one of the major pests of sugar beet. The identification of molecular markers associated with nematode tolerance would be helpful for developing tolerant varieties. The aim of this study was to identify single nucleotide polymorphism (SNP) markers linked to nematode tolerance from the Beta vulgaris ssp. maritima source WB242. A WB242-derived F2 population was phenotyped for host-plant nematode reaction revealing a 3:1 segregation ratio of the tolerant and susceptible phenotypes and suggesting the action of a gene designated as HsBvm-1. Bulked segregant analysis (BSA) was used. The most tolerant and susceptible individuals were pooled and subjected to restriction site associated DNA sequencing (RAD-Seq) analysis, which identified 7,241 SNPs. A subset of 384 candidate SNPs segregating between bulks were genotyped on the 20 most-tolerant and most-susceptible individuals, identifying a single marker (SNP192) showing complete association with nematode tolerance. Segregation of SNP192 confirmed the inheritance of tolerance by a single gene. This association was further validated on a set of 26 commercial tolerant and susceptible varieties, showing the presence of the SNP192 WB242-type allele only in the tolerant varieties. We identified and mapped on chromosome 5 the first nematode tolerance gene (HsBvm-1) from Beta vulgaris ssp. maritima and released information on SNP192, a linked marker valuable for high-throughput, marker-assisted breeding of nematode tolerance in sugar beet.

Sugar beet resistance to rhizomania: state of the art and perspectives.

The productivity of sugar beet is strongly limited by several biotic stresses, among them rhizomania (induced by Beet necrotic yellow vein virus, BNYVV) which causes yield losses of 20–50% or more. The only way to control this disease is the use of resistant varieties. Sources of resistances have been found in the ancestor of the cultivated beets Beta vulgaris L. ssp. maritima (L.) Arcang. Rz1 is the major resistance gene present within commercial sugar beet varieties. This resistance was recognized as monogenic and dominant. Experimental evidence highlighted that Rz1 originated from sea beets belonging to Munerati’s genetic pool. The development of molecular markers linked to Rz1 allows the use of marker assisted selection (MAS) to introgress this gene into pollinator lines, to assess the trueness of hybridity and to remove off-type individuals. MAS speeds variety development and reduces production costs guaranteeing at the same time a high qualitative standard in variety development. Recent studies have shown an emergence of new BNYVV strains with increased virulence that could overcome Rz1 resistance. Therefore, exploitation of new genetic sources of resistance and the pyramiding of several resistance genes into new breeding lines is becoming a main priority for sugar beet breeding companies to maintain an adequate resistance level to rhizomania.

Assessment of a selection pressure for improved nitrate and sulfate recovery by maize.

Abstract The increase in grain yield of current maize cultivars has been conditioned by the abundant supply of fertilizers, potentially involving energy waste and environment pollution. The shift from frugality to luxury consumption has been attributed to the scarce or zero selection pressure for improved nutrient recovery, due to the high fertility of soils usually adopted in breeding programs. Seven cycles of recurrent selection, starting from the same maize population and carried out on the same soil in conditions of either large (HF) or limited supply (LF) of macronutrients, have demonstrated the effectiveness of the selection pressure by reduced fertilizer application. Physiological parameters determined in seedlings growing in nutrient solution evidenced, in the LF population, a connection with both grain yield and efficiency of nitrate and sulfate recovery. Influx and efflux at steady supply or after deprivation, translocation to shoot, internal pool of both anions, and ATPase‐dependent H+ transpor...

Soil biological and biochemical traits linked to nutritional status in grapevine

The purpose of this work was to study vineyards of NE Italy seeking for features associated to the soil or plant compartment that could serve as proxies to infer productivity of the grape. Soils were characterized for physicochemical properties, mineralization of organic matter by a novel patented device based on in-situ microbial degradation of buried fibers, bacterial intergenic spacer length diversity (ARISA), enzyme activities and the expression of genes involved in response to abiotic stresses. Significant differences (p<0.05) were observed among vineyards for the parameters evaluated. The groupings obtained by ARISA were coherent with those obtained by PCA of soil properties. Vineyards endowed with higher productivity had soils showing higher enzyme activities along with neutral pH, higher TOC content and appropriate C/N ratio. These soils also showed higher mineralization of organic matter determined the novel in-soil thread degradation method. Grapevines of less productive vineyards had suboptimal leaf nitrogen and sulfur contents and showed up-regulation of WRKY, SuSy, PAL and STS1 genes. Results put in evidence useful correlations with yield that can be obtained up to several months earlier than harvest time upon analyzing selected indicators. An interesting link arises unifying soil biological properties, nutritional status, molecular stress response of grapevine and its production level. Keyword: Soil biological properties, edaphic stresses, nutritional status, molecular stress response

Effect of sulfate availability on root traits and microRNA395 expression in sugar beet

Nutritional stress is one of the main limits to sugar beet yield. This study evaluated morphological and molecular responses of sugar beet to changes in sulfate availability. Morphological characteristics of the root system and the accumulation of microRNA395 (miR395) were examined in sulfate(S)-supplemented and S-deprived seedlings under hydroponic conditions. We also investigated the functional role of miR395 in regulating the expression of APS1 gene coding for ATP-sulfurylase in roots and leaves. The S-deprived seedlings showed a significant increase in the number of root tips, in the miR395 expression in leaves but not in roots, and in the expression of APS1 gene. Our results indicate that miR395 may be a useful biomarker for sulfate status in sugar beet.

Sterol content and efficiency of ion uptake by roots of maize genotypes.

Data of compartmental analysis of sulphate were compared with the sterol content of roots of differently yielding maize genotypes. In conditions of steady state nutrient supply, sterol content was significantly correlated only with sulphate efflux (ϕco). This increased at increasing concentration of sterols in the roots. Influx to cytoplasm (ϕoc) was evaluated after sulphate deprivation leading to an induced rate of sulphate uptake. This was negatively correlated with sterol content, which was lower in the high than in the low yielding genotypes. When the highest yield genotype was grown at different sulphate concentrations, influx, efflux, root content of sulphate and sterols were positively correlated with the concentration of sulphate in the nutrient medium. Sterol content in roots appears to be controlled by both the genetic settlement and the nutritional status in maize. Low sterol content is connected with a high efficiency of sulphate utilization.