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Two branches of the lipoxygenase pathway seem to universally predominate in plants. One such pathway involves chain-cleavage of fatty acid hydroperoxides into aldehydes, and another is chain cyclization of a linolenic hydroperoxide with eventual transformation into jasmonates. The aldehyde pathway, which furnishes green-grassy or cucumber-like odors, is triggered by wounding or pathogen attack. The aldehydes generated are defensive against the growth of pathogenic bacteria/fungi. Recently, the aldehyde pathway has been extended to include the transformation of cis-3-hexenal and cis-3-nonenal into 4-hydroxy-2-hexenal and 4-hydroxy-2-nonenal, respectively, the latter of which are cytotoxic. The other pathway leads to the biosynthesis of the jasmonate phytohormones. The initial biosynthetic product, 7-isojasmonic acid, becomes converted into jasmonic acid, as well as a large family of related compounds. The jasmonates control diverse physiological processes, such as induction of proteins, defensive enzymes, tuberization, secondary metabolites, and senescence.
Abstract
The response of ‘White Cascade’ and ‘Coral Magic’ petunia (Petunia hybrida Vilm. -Andr.) plants to peroxyactyl nitrate (PAN) was tested 7 days after application of soil drenches of 0, 20, 40, 60, 80, 100, 120 μg benomyl/g drv weight of soil. The susceptible ‘White Cascade’, showed increased sensitivity to 745 μg/m3 PAN for 1.5 hr when soil was treated with benomyl levels of 60 μ/g soil or greater. Enhanced foilar response to PAN was similar at all concentrations of benomyl greater than 60 μ/g soil. Foliage of ‘White Cascade’ petunias treated with concentrations of benomyl below 60 μ/g soil, responded to PAN similarly to plants which were not treated with the fungicide. The PAN sensitivity of the tolerant ‘Coral Magic’ was unaffected by benomyl application.
Several unsaturated C6 and C9 aldehydes are released by broad bean (Vicia faba L.) tissues when wounded mechanically or by pathogens via lipoxygenase-catalyzed lipid oxidation. We examined the growth of isolated fungal cultures of the broad bean pathogens Colletotrichum truncatum, Rhizoctonia solani and Sclerotium rolfsii when exposed to several of these aldehydes. (2E)-Hexenal, (2E)-nonenal and (3Z)-nonenal were inhibitory to the growth of R. solani and S. rolfsii at 0.004 ul/ml or greater when applied as volatiles, although higher levels were required to inhibit C. truncatum. When applied directly in the growth medium, (2E)-4-hydroxy-2-nonenal was the most inhibitory compound tested, even though it had the least effect as a volatile.
Abstract
A preplant N application and the 2 irrigation methods most commonly used in Arizona to germinate commercially grown lettuce (Lactuca sativa L.) were studied in relation to the movement of soil NO3-N and total soluble salts (TSS) in lettuce beds. The intermittent pattern of irrigation resulted in highest levels of TSS at all sampling depths two weeks after the germination and emergence of the lettuce. Total soluble salts and NO3-N concentrations were increased by irrigation and were greatest in the surface 5 cm and center of the bed. Nitrogen application increased the amount of NO3-N found in the lettuce beds. Neither irrigation nor N treatment caused any accumulation of NO3-N in the area of the beds where the lettuce seedlings usually grow. The distribution patterns indicate that preplant N applications would be ineffective in meeting the early N needs of the plants.
Abstract
Higher yields, larger fruit size, and earlier maturity were achieved in muskmelons (Cucumis melo L.) by irrigating when soil moisture tensions at the 25-cm depth reached 50 and 75 kPa compared with tensions of 25 kPa. More fruits were culled in the wet treatment due to decay while the drier treatments produced more fruits with growth cracks. Melons from the drier treatments were higher in soluble solids. Irrigation did not affect the other storage and shipping quality factors measured. A prethinning irrigation caused restricted root development, vine growth, fruit size, and yield.
Abstract
The effectiveness of ammonium nitrate, ammonium sulfate, calcium nitrate and urea for winter grown head lettuce (Lactuca sativa L.) was evaluated. N source did not affect yield, quality factors, head size or total N accumulation. Applications of fertilizers containing NO3-N resulted in slightly higher NO3-N concentrations in the midribs. Plant growth and N accumulation were similar with all N sources at low temperatures. Air temperature below 13°C for a week or more sharply reduced N uptake and plant growth with all sources. About 80% of the total N is taken up by the plants in the 4 weeks before harvest. N source did not affect quality.
Abstract
Parental, F1, F2, and backcross generations of tomato (Lycopersicon esculentum Mill.) lines Morden MEL2668170G (MEL) and ‘Walter’ (WA) were screened as seedlings for resistance to verticillium wilt (Verticillium dahliae Kleb.) race 2. Disease reaction means, based on the number of leaves and cotyledons with symptoms 5.5 weeks after inoculation, were 2.7 for MEL and 4.6 for WA. Resistance in MEL appeared to be recessive with narrow sense heritability estimated at 0.25 or less. Disease severity was sometimes inadequate to avoid the selection of escapes in advanced generations. Analysis of F3 progenies, however, indicated 3 genes or less might be involved. Results suggest race-2 resistance can be maintained in advanced generations by the elimination of highly susceptible plants and by progeny testing to insure recovery of the most resistant individuals rather than escapes.
Pointed blossom-end morphology may be used to reduce blossom-end scar size in large-fruited, fresh-market tomatoes (Lycopersicon esculentum Mill.). The usefulness of this characteristic has been limited due to persistence of pointedness on mature fruit, resulting in postharvest bruising, and to close association of pointedness with leaf curl, which may increase foliar disease problems. The inheritance of pointedness in three breeding lines (NC 140, Fla 890559-24, and Fla 894413-1) and four accessions with previously described blossom-end morphology genes [LA 2-5 with persistent style (pst), LA 986 with beaky (bk), LA 1787 with beaky-2 (Bk-2), and LA 2353 with nipple tip (n)] was investigated. In F1 s and F2s of crosses with wild types, some pointedness was observed in heterozygotes, but the level of expression was generally close to wild type expression, except for LA 986. Consequently, Bk-2 in LA 1787 was renamed bk-2. F1 complementation tests were difficult to interpret. Wild types segregated in F2s of all complementation crosses, except for LA 986 × LA 2-5, a result indicating the presence of the same gene in these two accessions. Three new nipple-tip genes were named; n-2 in NC 140, n-3 in Fla 890559-24, and n-4 in Fla 894413-1. None of the seven accessions tested had significant leaf curl. Early identification of mutant plants by the shape of the stylar base in flowers at anthesis was reliable only for bk. Various blossom-end morphology genes may be backcrossed into otherwise desirable breeding lines, and complementing parents may be intercrossed to obtain optimal smoothness in the hybrid without undesirable pointed mature hybrid fruit.