Cultivars levels

Plants are continually exposed to a vast array of potential phytopathogenic fungi nevertheless, plants resist to most of them by blocking fungal development soon after penetration. Resistance against pathogens can be distinguished in resistance at the species level (non-host resistance) and resistance at the cultivar level (race-cultivar resistance). Plants lack a circulatory system and antibodies and have evolved a defense mechanism that is distinct from the vertebrate immune... 

Table I. Monoterpenes found, in 3 blackcurrant cultivars (levels in...

Among 19 cultivars of carrots, the contents of P-carotene varied from 46 to 103 pg/g and of a-carotene from 22 to 49 pg/g. Carrots of the cultivar Nantes grown in Brazil showed the lowest level and an unspecified cultivar from Spain had intermediate levels of both carotenes (Tables 4.2.1 and 4.2.2). The distribution of a- and p-carotene isomers in fresh carrots was investigated. Results reported included the absence of a- and P-carotene cis isomers in unspecified cultivars, 3% of 9-c -p-carotene and 3% of 9-c -a-carotene in cultivar Nantes, 9% of 9-... 

Lycopene is well known as the predominant carotene in tomatoes, accounting for 65 to 98% of the total colored carotenoid content, depending on the cultivar (Table 4.2.3). The levels of lycopene in fresh tomatoes for salad varied from 21 to 79 g/g 34,35 jjj tomatoes for processing and deep-red tomatoes, the level of lycopene can be as high as 623 More than 80% of the tomatoes produced are... 

Amounts and relative proportions depend on species, cultivars, environmental conditions, health, age, level of chemical, physical and biological stress, and so on. 

Aluminium toxicity is a major stress factor in many acidic soils. At soil pH levels below 5.0, intense solubilization of mononuclear A1 species strongly limits root growth by multiple cytotoxic effects mainly on root meristems (240,241). There is increasing evidence that A1 complexation with carboxylates released in apical root zones in response to elevated external Al concentration is a widespread mechanism for Al exclusion in many plant species (Fig. 10). Formation of stable Al complexes occurs with citrate, oxalate, tartarate, and—to a lesser extent— also with malate (86,242,243). The Al carboxylate complexes are less toxic than free ionic Al species (244) and are not taken up by plant roots (240). This explains the well-documented alleviatory effects on root growth in many plant species by carboxylate applications (citric, oxalic, and tartaric acids) to the culture media in presence of toxic Al concentrations (8,244,245) Citrate, malate and oxalate are the carboxylate anions reported so far to be released from Al-stressed plant roots (Fig. 10), and Al resistance of species and cultivars seems to be related to the amount of exuded carboxylates (246,247) but also to the ability to maintain the release of carboxylates over extended periods (248). In contrast to P deficiency-induced carboxylate exudation, which usually increases after several days or weeks of the stress treatment (72,113), exudation of carboxylates in response to Al toxicity is a fast reaction occurring within minutes to several hours... 

Figure 16 Cumulative phosphorus uptake curves (per unit root length) predicted for two tomato cultivars Knox and C37 ) grown in a soil fertilised to two P-levels. (From Ref. 28.)...

Figure 17 Predicted changes in the relative growth rates of two tomato cultivars grown under sufficient and insufficient levels of phosphorus. The inset shows the changes in root mass plant mass ratio of the cultivars in the low-P soil. (From Ref. 28.)...

There is very little information on cultivar differences with respect to (i) resistance to infection by P. verrucosum and (ii) OTA formation (Hokby et al., 1979 Axberg el al., 1997). The latter performed a laboratory experiment with six artificially inoculated cultivars of barley and three of wheat. After incubation for 23 weeks at approximately 19% moisture, the barley cultivars contained between 6 and 350 and the wheat cultivars between 25 and 890 ng OTA g 1 grain. In another study, Elmholt and Rasmussen (2005) reported that two of four cultivars of spring spelt from the same field contained 18 and 92 ng OTA g 1, respectively, while the other two contained less than 0.5 ng OTA g As differences in OTA neither correlated with moisture content at harvest nor with the level of P. verrucosum, they were probably caused by differences in cultivar sensitivity. This should, however, be further studied. 

Andrivon, D., Lucas, J.M. and Ellisseche, D. (2003). Development of natural blight epidemics in pure and mixed plots of potato cultivars with different levels of partial resistance , Plant Pathology, 52, 586-596. 

Exposure to volatile stress signals such as ethylene and jasmonic acid can induce the synthesis and accumulation of high levels of phenolic compounds. The effect is not readily apparent because the accumulated phenolic compounds remain sequestered in organelles within the induced cells. However, increased membrane permeability resulting from even a minor injury or stress can result in levels of discoloration that are abnormally high for that cultivar. 

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