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  • Author or Editor: Wayne H. Loescher x
  • Journal of the American Society for Horticultural Science x
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Abstract

Nonstructural carbohydrates of sweet cherry (Prunus avium L. ‘Bing’) changed dramatically both qualitatively and quantitatively during the year. In perennial tissues, total nonstructural carbohydrates (TNC) were highest at leaf abscission. TNC increased sharply in spurs at budbreak, but, in other perennial tissues, reserves decreased with or before budbreak. TNC in all but spurs were least, e.g., 2% to 4% of fall levels, shortly after full bloom, but then immediately began to increase. Accumulations slowed during the last 4 to 6 weeks of fruit growth and then increased after harvest. Prebloom decreases and postbloom increases occurred earlier in 1- and 2-year-old shoots when compared to trunk or root tissues. Starch was the most common storage material. During winter, interconversion of starch and soluble carbohydrates in wood of the trunk and 1- and 2-year-old shoots was apparent. Sucrose was the predominant soluble carbohydrate during dormancy, but sorbitol dominated during active growth. Raffinose was present only during dormancy, and inositol only when leaves were present. Because sweet cherry flowers and fruits early, carbohydrate reserves could critically affect productivity.

Open Access

Abstract

Extraction and assay of sorbitol dehydrogenase (SDH) throughout fruit maturation of 3 apple (Malus domestica Borkh.) cultivars, watercore-resistant ‘Golden Delicious,’ occasionally susceptible ‘McIntosh’, and normally susceptible ‘Starkrimson,’ showed no relationship between susceptibility to watercore and extractable enzyme activity. There was, however, a relationship between increased SDH activity and onset of the climacteric as measured by ethylene and CO2 evolution, suggesting that SDH, like certain other enzymes, increases during maturation.

Open Access

Abstract

Mesocarp development of peach [Prunus persica (L.) Batsch cv. Redhaven] as measured by fresh weight and size increase, progressed along a double sigmoid curve which was reflected in the activity of extractable wall-associated α- and β-nitrophenylgalactosidases. Enzyme activities, both on protein and dry weight basis, rose rapidly during early fruit development, leveled off, then again rose rapidly at maturation. There was more α-nitrophenylgalactosidase activity than β-nitrophenylgalactosidase activity throughout development. Increases in both galactosidases followed rather than preceded increases in size. The final increases were, however, well correlated with fruit maturation.

Open Access

Grafting is a well-established agricultural practice, and it now has implications for the commercialization of transgenic plants. In transgrafted plants, only one part (scion or rootstock) is transgenic with the other part untransformed. However, transgenes may affect both mobile and immobile endogenous metabolites (e.g., RNAs, proteins, and phytohormones) and mobility has implications for transgrafting. In the phloem, long-distance transport of mobile metabolites can play important roles in plant development and signaling. In a transgrafted plant, an immobile transgene product (ITP) is not likely to be translocated across the graft union. In contrast, mobile transgene products (MTP) may be translocated across the graft. Regardless of the mobility of transgene products (TP), interaction of transgenic and nontransgenic parts in transgrafted plants through either the MTP or ITP has been demonstrated to be effective in facilitating changes in nontransgenic portions of the plant. Consequently, and particularly in fruit crops, transgrafting provides the potential for improving products from their nontransgenic parts with the possibility of minimizing the controversy over transgenic crops. This review focuses mainly on the mobility of TP and effects on the whole transgrafted plant.

Free access

A preliminary understanding of developmental processes among divergent species is essential to evaluate the applicability of information from model species to plants of agricultural importance. In tomato (Lycopersicon esculentum Mill.), where the molecular biology associated with fruit ripening has been studied most extensively, tissue softening is due at least in part to the activity of proteins called expansins, in concert with enzymatic activities that modify the pectin and xyloglucan components of the cell wall. We evaluated the potential for the concerted action of expansins and other cell wall-modifying enzymes during ripening in a highly divergent fruit species, sour cherry (Prunus cerasus L.). We identified a family of four expansin genes that was strongly upregulated at the advent of ripening. Activation of these genes was accompanied by strong upregulation of gene(s) encoding potential pectin methylesterases, pectate lyase(s), and xyloglucan endotransglycosylase(s). Initiation of ripening and gene induction were also associated with a rapid decrease in cell wall weight. These results suggest that expansin and several other distinct activities could be involved in ripening-associated cell wall modification in cherries.

Free access

Drought is an important abiotic stress that limits common bean (Phaseolus vulgaris) productivity. The objective of this study was to determine shoot traits that are associated with drought tolerance in common bean seedlings. Ten common bean genotypes consisting mainly of cultivars and breeding lines from the Mesoamerican race of the Middle American gene pool were first evaluated in the greenhouse. Genotypes were grown in a shallow soil profile to limit root growth and assess shoot phenotypes under stress. Water stress was imposed by withholding watering for 24 days after planting. Traits evaluated included wilting, unifoliate senescence, stem greenness, and recovery from drought. Biomass and number of pods/plant produced after drought recovery were evaluated to quantify the effect of early drought stress on bean growth and reproduction. A second group of 94 common bean genotypes from the Bean Coordinated Agricultural Project (BeanCAP) were evaluated using the same protocol to determine the genetic variability for the same traits in a wider range of genotypes. In general, genotypes known to possess drought avoidance in the field conferred by deep rooting traits performed poorly in these conditions suggesting that the assay could be used to identify seedling shoot traits that contribute to drought tolerance. Genotypes from race Mesoamerica showed the greatest range in wilting. Genotypes that showed a slow rate of wilting maintained a green stem and had a higher recovery rate after watering. Importantly, these genotypes demonstrated a smaller reduction in biomass and pod number under stress compared with non-stress treatments. A few genotypes recovered completely despite expressing severe wilting, whereas the majority of genotypes with high wilting rates did not recover. Among the BeanCAP materials, genotypes bred in the rainfed midwestern United States showed overall better recovery than those bred under the irrigated production system used in the western United States. Because recovery from drought is a prerequisite to plant regrowth, biomass, and pod production after drought stress, factors that contribute to recovery were studied. Stem greenness was highly positively correlated to the recovery, whereas wilting was negatively correlated to the recovery. In a regression analysis, stem greenness and slow wilting were found to be important contributors to the variability of recovery. In addition, photosynthetic rate and stomatal conductance (g S) explained variation in wilting and stem greenness. These results suggest that wilting and stem greenness might be useful traits to screen for drought tolerance in seedlings of common bean.

Free access

Abstract

Source–sink relationships in sweet cherry were altered by girdling limbs both above and below fruiting spurs. Spurs isolated by girdling both above and below had lower total fruit weight per spur and lower weight per fruit then those above or below girdles. Fruit number per spur was not altered, but soluble solids and fruit color were lower in fruits from isolated spurs than fruit from spurs either above or below girdles. Fruit on spurs above girdles were generally highest in soluble solids and fruit color. These factors indicate fruit on isolated spurs also were delayed in maturity. Spurs below girdles were unaffected by girdling. Girdling had no effect on spur leaf net photosynthesis, stomatal conductance, or fruit water loss rate. The results indicate that spur leaves alone do not have the capacity to support fruit growth in sweet cherry and must, therefore, be supplemented by photosynthates from other sources.

Open Access

Abstract

A controlled environment study was conducted to determine if ‘Russet Burbank’ potatoes (Solanum tuberosum L.) were more tolerant of NH4-N as established plants than as young plants. When grown on one N source for 86 days, root and shoot growth were best with NO3-N, intermediate with NH4 + NO3, and least with NH4-N. Changing the N source from NO3-N or NH4 + NO3 to NH4-N at tuber initiation (58 days after planting) reduced both shoot and root growth. Conversely, changing the N source from NH4-N to NH4 + NO3 improved growth. The highest tuber weights were obtained with continuous NH4 + NO3 or when NH4-N was applied at tuber initiation to plants previously grown on NO3-N alone. Nitrogen source also influenced absorption of other nutrients. Changing the N source once plants were established, however, did not have a consistent effect on mineral composition. We conclude that when NH4-N is the sole form of N available to the plant, it is detrimental to potato growth regardless of stage of development.

Open Access