Differentiating Oriental Fruit Moth and Codling Moth (Lepidoptera: Tortricidae) Larvae Using Near-Infrared Spectroscopy.

Cydia pomonella (L.) and Cydia molesta (Busck) (Lepidoptera: Tortricidae) are two important lepidopteran pests that may co-occur in apple orchards and are difficult to differentiate in the larval stage. We investigate the possibility of using near-infrared spectroscopy (NIRS) coupled with partial least squares analysis to distinguish the larvae of the two species. We further assess whether wild individuals can be differentiated using laboratory strains of the two species for model calibration. The NIRS spectra of C. molesta and C. pomonella differed most in the wavelengths between 1,142 and 1,338 nm. Using these wavelengths, partial least squares analysis allowed the differentiation of C. molesta and C. pomonella at the larval stage with very low error, but only as long as both the calibration and prediction sets for individuals had the same origin (either both from the laboratory or both from the field). Errors that appeared when using laboratory individuals for calibration were owing to the divergence of the C. pomonella laboratory strain, most likely following evolution during rearing. Thus, NIRS appears to be a promising tool for the easy and rapid identification of individuals in the field, provided that it is calibrated based on a subset of field individuals.

Combining ecophysiological modelling and quantitative trait locus analysis to identify key elementary processes underlying tomato fruit sugar concentration.

A mechanistic model predicting the accumulation of tomato fruit sugars was developed in order (i) to dissect the relative influence of three underlying processes: assimilate supply (S), metabolic transformation of sugars into other compounds (M), and dilution by water uptake (D); and (ii) to estimate the genetic variability of S, M, and D. The latter was estimated in a population of 20 introgression lines derived from the introgression of a wild tomato species (Solanum chmielewskii) into S. lycopersicum, grown under two contrasted fruit load conditions. Low load systematically decreased D in the whole population, while S and M were targets of genotype × fruit load interactions. The sugar concentration positively correlated to S and D when the variation was due to genetic introgressions, while it positively correlated to S and M when the variation was due to changes in fruit load. Co-localizations between quantitative trait loci (QTLs) for sugar concentration and QTLs for S, M, and D allowed hypotheses to be proposed on the processes putatively involved at the QTLs. Among the five QTLs for sugar concentration, four co-localized with QTLs for S, M, and D with similar allele effects. Moreover, the processes underlying QTLs for sugar accumulation changed according to the fruit load condition. Finally, for some genotypes, the processes underlying sugar concentration compensated in such a way that they did not modify the sugar concentration. By uncoupling genetic from physiological relationships between processes, these results provide new insights into further understanding of tomato fruit sugar accumulation.

A model describing cell polyploidization in tissues of growing fruit as related to cessation of cell proliferation.

Endoreduplication is a phenomenon, widespread among plants, which consists of an incomplete cell cycle without mitosis and leads to the increase of the nuclear DNA content. In this work, a model was developed describing cell proliferation and DNA endoreduplication over the whole fruit development, from the pre-anthesis period until maturation. In each mitotic cycle of duration tau, the proportion of cells proceeding through division depends on a constant parameter rho and on the progressive decline of the proliferating capacity . The non-dividing cells may either stop the reduplication fully, or switch to repeated syntheses of DNA without cell division, resulting in cell endoreduplication. A single constant parameter sigma describes the proportion of cells that moves from one to the next class of DNA content after each lapse of time tauE, considered to be the minimum time required for an endocycle. The model calculates the total number of cells and their distribution among eight classes of ploidy level. The dynamic patterns of cell proliferation and ploidy were compared with those obtained experimentally on two contrasting tomato genotypes. The approach developed in this model should allow the future integration of new knowledge concerning the genetic and environmental control of the switch from complete to incomplete cell cycle.