Grain amaranths are defoliation tolerant crop species capable of utilizing stem and root carbohydrate reserves to sustain vegetative and reproductive growth after leaf loss.

Tolerance to defoliation can be defined as the degree to which productivity is affected by photosynthetic area reduction. This trait was studied in grain amaranth (Amaranthus cruentus and A. hypochondriacus), which are considered to be a highly defoliation-tolerant species. The physiological and biochemical responses to increasing levels of mechanical leaf removal up to total defoliation were quantified. Tolerance appeared to be dependent on various factors: ( i) amount of lost tissue; (ii) mechanics of leaf tissue removal; (iii) environment, and (iv) species tested. Thus, grain amaranth was found to be a highly tolerant species under green-house conditions when leaf tissue loss was performed by gradual perforation. However, tolerance was compromised under similar conditions when defoliation was done by gradual cutting of the leaf. Also tolerance in completely defoliated plants tended to decrease under field conditions, where differences between A. cruentus and A. hypochondriacus were observed. All non-structural carbohydrate (NSC) levels were reduced in stems and roots of totally defoliated amaranths one day after treatment. Such depletion probably provided the carbon (C) resources needed to sustain the early recovery process in the absence of photosynthetic capacity. This was corroborated by shading of intact plants, which produced the same rapid and drastic reduction of NSC levels in these tissues. These results emphasize the role of stored NSCs, particularly starch, in buffering the impact of severe defoliation in amaranth. The fall in sucrose synthase and cell wall invertase activity observed in stems and roots soon after defoliation was consistent with their predicted shift from sink to source tissues. It is concluded that mobilization of C stores in stems and roots, is a physiologically important trait underlying tolerance to defoliation in grain amaranth

Genetic mapping identifies loci that influence tomato resistance against Colorado potato beetles

"The Colorado potato beetle (CPB; Leptinotarsa decemlineata Say), the most economically important insect pest on potato (Solanum tuberosum L.), also feeds on other Solanaceae, including cultivated tomato (Solanum lycopersicum L.). We used tomato genetic mapping populations to investigate natural variation in CPB resistance. CPB bioassays with 74 tomato lines carrying introgressions of Solanum pennellii in S. lycopersicum cv. M82 identified introgressions from S. pennellii on chromosomes 1 and 6 conferring CPB susceptibility, whereas introgressions on chromosomes 1, 8 and 10 conferred higher resistance. Mapping of CPB resistance using 113 recombinant inbred lines derived from a cross between S. lycopersicum cv UC-204B and Solanum galapagense identified significant quantitative trait loci on chromosomes 6 and 8. In each case, the S. galapagense alleles were associated with lower leaf damage and reduced larval growth. Results of both genetic mapping approaches converged on the same region of chromosome 6, which may have important functions in tomato defense against CPB herbivory. Although genetic mapping identified quantitative trait loci encompassing known genes for tomato acyl sugar and glycoalkaloid biosynthesis, experiments with acyl sugar near-isogenic lines and transgenic GAME9 glycoalkaloid-deficient and overproducing lines showed no significant effect of these otherwise insect-defensive metabolites on CPB performance.

Effect of defoliation on phenological parameters in grain amaranth grown in the greenhouse.

<p>45-day-old <i>A. cruentus</i> plants were subjected to 4 defoliation degrees: 0%, 20%, 50% and 100% Phenological parameters, A shoot; B root, C plant height, and D stem thickness, were measured at 1, 30 an110 d after treatment. Each bar represents the mean ± SE (n = 10). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for the Dunnett test.</p

Effect of defoliation on grain amaranth growth and yield in green house.

<p>Plants from different cultivars (<i>Tarasca, Dorada Amaranteca,n utrisol, Revancha</i> and <i>Gabriela</i> ) were grown equally in the green house and at panicle emergence were subjected to 2 defoliation treatments: control (0%) and 100% defoliation. Phenological parameters were measured at physiological maturity: A plant height; B shoot dry weight; C seed yield and D harvest index. Each bar represents the mean ± SE (n = 10). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for the Dunnett test.</p

Seed composition in defoliated amaranth in green house.

<p>At mature amaranth seeds were collected and analyzed for A 100 seeds weight, B seed starch, C seed lipids and D seed protein. Each bar represents the mean ± SE (n = 10). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for t Test.</p

Carbohydrate levels in the stem of defoliated and undamaged amaranth plants.

<p>Plants were harvested at 1, 30 and 110 days after treatment. A glucose, B fructose, C sucrose and D starch. Each bar represents the mean ± SE (n = 10). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for Dunnett Test.</p

Effect of defoliation on amaranth's reproductive yield.

<p>A Panicle dry weight. B Seed yield at maturity, C Calculated panicle index as the ratio of seed weight and panicle weight. Each bar represents the mean ± SE (n = 10). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for the Dunnett test.</p

Seed composition in defoliated amaranth in the field.

<p>At mature amaranth seeds were collected and analyzed for A 100 seeds weight, B seed starch, C seed lipids and D seed protein. Each bar represents the mean ± SE (n = 5). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for the Dunnett test.</p

Carbohydrate levels in the roots of defoliated and undamaged amaranth plants.

<p>Plants were harvested at 1, 30 and 110 days after treatment. A glucose, B fructose, C sucrose and D starch. Each bar represents the mean ± SE (n = 10). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for Dunnett Test.</p

Effect of defoliation on grain amaranth growth and yield in field.

<p>Plants from different cultivars (<i>Amaranteca</i>, <i>Dorada</i>, <i>Nutrisol</i> and <i>Revancha</i>) were grown equally in the field and at panicle emergence were subjected to 3 defoliation treatments: control (0%), 50%, and 100% defoliation. Phenological parameters were measured at physiological maturity: A plant height; B shoot dry weight; C seed yield and D harvest index. Each bar represents the mean ± SE (n = 5). The asterisks over the bars represent statistical significance at * <i>p</i> = 0.05, ** <i>p</i> = 0.01, *** <i>p</i> = 0.001 for the Dunnett test.</p