Model-assisted evaluation of crop load effects on stem diameter variations and fruit growth in peach

Key message: The paper identifies and quantifies how crop load influences plant physiological variables that determine stem diameter variations to better understand the effect of crop load on drought stress indicators. Stem diameter (D (stem)) variations have extensively been applied in optimisation strategies for plant-based irrigation scheduling in fruit trees. Two D (stem) derived water status indicators, maximum daily shrinkage (MDS) and daily growth rate (DGR), are however influenced by other factors such as crop load, making it difficult to unambiguously use these indicators in practical irrigation applications. Furthermore, crop load influences the growth of individual fruits, because of competition for assimilates. This paper aims to explain the effect of crop load on DGR, MDS and individual fruit growth in peach using a water and carbon transport model that includes simulation of stem diameter variations. This modelling approach enabled to relate differences in crop load to differences in xylem and phloem water potential components. As such, crop load effects on DGR were attributed to effects on the stem phloem turgor pressure. The effect of crop load on MDS could be explained by the plant water status, the phloem carbon concentration and the elasticity of the tissue. The influence on fruit growth could predominantly be explained by the effect on the early fruit growth stages

SNP markers tightly linked to root knot nematode resistance in grapevine (<i>Vitis cinerea</i>) identified by a genotyping-by-sequencing approach followed by Sequenom MassARRAY validation

<div><p>Plant parasitic nematodes, including root knot nematode <i>Meloidogyne</i> species, cause extensive damage to agriculture and horticultural crops. As <i>Vitis vinifera</i> cultivars are susceptible to root knot nematode parasitism, rootstocks resistant to these soil pests provide a sustainable approach to maintain grapevine production. Currently, most of the commercially available root knot nematode resistant rootstocks are highly vigorous and take up excess potassium, which reduces wine quality. As a result, there is a pressing need to breed new root knot nematode resistant rootstocks, which have no impact on wine quality. To develop molecular markers that predict root knot nematode resistance for marker assisted breeding, a genetic approach was employed to identify a root knot nematode resistance locus in grapevine. To this end, a <i>Meloidogyne javanica</i> resistant <i>Vitis cinerea</i> accession was crossed to a susceptible <i>Vitis vinifera</i> cultivar Riesling and results from screening the F₁ individuals support a model that root knot nematode resistance, is conferred by a single dominant allele, referred as <i>MELOIDOGYNE JAVANICA RESISTANCE1 (MJR1)</i>. Further, <i>MJR1</i> resistance appears to be mediated by a hypersensitive response that occurs in the root apical meristem. Single nucleotide polymorphisms (SNPs) were identified using genotyping-by-sequencing and results from association and genetic mapping identified the <i>MJR1</i> locus, which is located on chromosome 18 in the <i>Vitis cinerea</i> accession. Validation of the SNPs linked to the <i>MJR1</i> locus using a Sequenom MassARRAY platform found that only 50% could be validated. The validated SNPs that flank and co-segregate with the <i>MJR1</i> locus can be used for marker-assisted selection for <i>Meloidogyne javanica</i> resistance in grapevine.</p></div