Low Acid Cultivars Research Articles

Assessment of organic acid accumulation and its related genes in peach

Fruit acidity is an important determinant of peach organoleptic quality, but its regulatory mechanism remains elusive. Measurement of organic acids in ripe fruits of seventy-five peach cultivars revealed the predominant components malate and citrate, accompanied by quinate. Organic acid accumulation increased at early stages of fruit growth, but exhibited a more dramatic reduction in low-acid cultivar during later stages of fruit development compared to high-acid cultivars. Low-acid cultivars showed citrate degradation and less transport of malate into the vacuole due to up- and down-regulation of a GABA pathway gene GAD and a malate transporter gene ALMT9, respectively. The NAD-MDH1 gene might control the rate-limiting step in malate synthesis, while three genes, PDK, PK, and ADH, could affect citrate synthesis through the pyruvate-to-acetyl-CoA-to-citrate pathway. Altogether, these results suggested that malate accumulation is controlled at the level of metabolism and vacuolar storage, while metabolism is crucial for citrate accumulation in peach.

Breeding grapevines for tropical environments

Grapevines are increasingly grown in the latitudes between the Tropics of Cancer and Capricorn. In many cases environments modified by elevation are utilized to create temperate growing conditions. The majority of tropical grapes are consumed fresh but some are dried (India) and others are made into wine (Brazil, Venezuela). Currently most plantings are of pure Vitis vinifera varieties. Early ripening, low acid cultivars such as Cardinal, Perlette, Ribier and Thompson Seedless which have a relatively short cycle between budburst and harvest are commonly used, and pruning is timed to ensure maturation before the onset of heavy tropical rains. Other V. vinifera varieties used in the tropics such as Muscat Hamburg, Teneron, Anab-e-Shahi, and Italia have bunch and skin characteristics that give them some resistance to rain damage. There are a number of grapevine varieties that are hybrids between V. vinifera and other Vitis species which are currently grown in the tropics. These have some degree of resistance to fungal diseases and include Isabella, Kyoho, Delaware, Himrod, Campbell Early ( V. labrusca hybrids), the Criolla hybrids (V. caribaea hybrids and Villard blanc (a complex French hybrid based on American species). There is considerable scope to increase the resistance of grapes to the main fungal diseases encountered in the tropics such as downy and powdery mildew, anthracnose and bunch rots by using a range of Vitis species as parents. These hybrids should be based on species that do not give strong 'foxy' flavours and could involve complex French hybrids, V. rotundifolia and also Asian species such as V. amurensis and V. armata . CSIRO Merbein has a small hybridisation program aimed at developing new varieties for tropical environments.

Citrus PH5-like H(+)-ATPase genes: identification and transcript analysis to investigate their possible relationship with citrate accumulation in fruits.

PH5 is a petunia gene that encodes a plasma membrane H+-ATPase and determines the vacuolar pH. The citrate content of fruit cell vacuoles influences citrus organoleptic qualities. Although citrus could have PH5-like homologs that are involved in citrate accumulation, the details are still unknown. In this study, extensive data-mining with the PH5 sequence and PCR amplification confirmed that there are at least eight PH5-like genes (CsPH1-8) in the citrus genome. CsPHs have a molecular mass of approximately 100 kDa, and they have high similarity to PhPH5, AtAHA10 or AtAHA2 (from 64.6 to 80.9%). They contain 13–21 exons and 12–20 introns and were evenly distributed into four subgroups of the P3A-subfamily (CsPH1, CsPH2, and CsPH3 in Group I, CsPH4 and CsPH5 in Group II, CsPH6 in Group IV, and CsPH7 and CsPH8 in Group III together with PhPH5). A transcript analysis showed that CsPH1, 3, and 4 were predominantly expressed in mature leaves, whereas CsPH2 and 7 were predominantly expressed in roots, CsPH5 and 6 were predominantly expressed in flowers, and CsPH8 was predominantly expressed in fruit juice sacs (JS). Moreover, the CsPH transcript profiles differed between orange and pummelo, as well as between high-acid and low-acid cultivars. The low-acid orange “Honganliu” exhibits low transcript levels of CsPH3, CsPH4, CsPH5, and CsPH8, whereas the acid-free pummelo (AFP) has only a low transcript level of CsPH8. In addition, ABA injection increased the citrate content significantly, which was accompanied by the obvious induction of CsPH2, 6, 7, and 8 transcript levels. Taken together, we suggest that CsPH8 seems likely to regulate citrate accumulation in the citrus fruit vacuole.

Physicochemical properties and aroma volatile profiles in a diverse collection of California-grown pomegranate (Punica granatum L.) germplasm

Colorful antioxidant-rich fruits often convey astringency and sourness that juice consumers may not appreciate. We assessed properties in juices from a collection of California-grown pomegranate from the National Clonal Germplasm Repository. The goal was to evaluate overall differences in germplasm with quality traits classified as sweet, sweet–sour and sour. Previous relationships noted in sweet and sour cultivar attributes were observed. Wonderful generally clustered with sweet–sour and sour cultivars. Sweet low acid cultivars occasionally clustered closely with Wonderful which is hard to rationalize. The dominant compounds were 3-hexenol and 1-hexanol which allowed separation of Kara Gul, Haku-botan and Wonderful. Aldehyde and terpene content can be used to characterize cultivars. The study represents the first data on variation in juice qualities in different sweet, sweet–sour and sour cultivars, grown in California, compared with Wonderful. Data may help the juice industry better select raw juice materials in order to ultimately satisfy consumers.

Relationship between ripe soluble solids concentration (RSSC) and consumer acceptance of high and low acid melting flesh peach and nectarine ( Prunus persica (L.) Batsch) cultivars

The minimum RSSC needed to reach high consumer acceptance for peach and nectarine was determined by using ‘in-store’ consumer tests of low and high RTA melting flesh cultivars as a part of our program to develop minimum quality indexes. For ‘Ivory Princess’, a low acid, white flesh peach, ‘Honey Kist’, a low acid, yellow flesh nectarine, ‘Elegant Lady’, a high acid, yellow flesh peach, and ‘Spring Bright’, a high acid, yellow flesh nectarine, degree of liking and consumer acceptance were associated with ripe soluble solids concentration (RSSC) regardless of ripe titratable acidity (RTA). For the two high acid (0.70–0.90% RTA) cultivars tested, consumer acceptance increased rapidly as RSSC increased, reaching ∼90%. In these cultivars, consumer acceptance reached a plateau and above which, it became insensitive to any additional increase in RSSC. For ‘Elegant Lady’ and ‘Spring Bright’, the plateau was reached at 11–12%, and 10–11% RSSC with ∼90% consumer acceptance, respectively. For the low acid cultivars (0.30–0.50% RTA), ‘Ivory Princess’ and ‘Honey Kist’, consumer acceptance progressively increased as RSSC increased without reaching a plateau, and attained nearly 100% acceptance with RSSC of 16 and 15%, respectively. For these low acid and high acid cultivars, consumer acceptance was closely related to RSSC but maximum consumer acceptance was attained at different RSCC levels depending on the cultivar. The fact that these cultivars reached high consumer acceptance with different RSSC levels indicates that a single generic RSSC quality index would not be reliable to assure consumer satisfaction across all cultivars.

Relationship of acid phosphatase activity and Brix/acid ratio in cherries

This research was undertaken to determine the relationship of acid phosphatase and Brix/acid ratio in cherries. High-acid cultivars of cherries (Karneol, Northstar, Kroeker, Danube, Montmorency, Oblinska, and Topas) exhibited low Brix/acid ratios while low-acid cultivars of cherries (Balatron, Sweetheart, Hedelfingen, and Hudson) had high Brix/acid ratios. The values of correlation coefficient ( r 2 ) for acid phosphatase and Brix/acid ratio in different cultivars grown in 2003 and 2004 were 0.88 and 0.84, respectively. An inverse relationship appeared to exist between the acid phosphatase activity and the acidity in cherries, and the r 2 values for 2003 and 2004 crops were 0.97 and 0.81, respectively. The plot of acid phosphatase vs. Brix in cherries showed a positive slope, and the r 2 values for 2003 and 2004 crops were 0.89 and 0.88, respectively. The results of this study indicate that acid phosphatase could serve as a marker for breeding new fruit cultivars with a desirable Brix/acid ratio.

Relationship of acid phosphatase activity and Brix/acid ratio in apples

This research was undertaken to determine the relationship of acid phosphatase and Brix/acid ratio in apples. High-acid cultivars of apples (Zapata, Cap of Liberty, and Edward VII) exhibited low Brix/acid ratios while low-acid cultivars of apples (Empire and Idared) had high Brix/acid ratios. The coefficient of correlation ( r 2) for acid phosphatase and Brix/acid ratio in apples was calculated to be 0.96. An inverse relationship appeared to exist between the acid phosphatase activity and the acidity in apples ( r 2=0.83). The results of this study indicate that acid phosphatase could serve as a marker for breeding new fruit cultivars with a desirable Brix/acid ratio.

Isolation and characterization of six peach cDNAs encoding key proteins in organic acid metabolism and solute accumulation: involvement in regulating peach fruit acidity.

As in many other fleshy fruits, the predominant organic acids in ripe peach (Prunus persica (L.) Batsch) fruit are malic and citric acids. The accumulation of these metabolites in fruit flesh is regulated during fruit development. Six peach fruit-related genes implicated in organic acid metabolism (mitochondrial citrate synthase; cytosolic NAD-dependent malate dehydrogenase, and cytosolic NADP-dependent isocitrate dehydrogenase) and storage (vacuolar proton translocating pumps: one vacuolar H+-ATPase, and two vacuolar H+-pyrophosphatases) were cloned. Five of these peach genes were homologous to genes isolated from fruit in other fleshy fruit species. Phylogenetic and expression analyses suggested the existence of a particular vacuolar pyrophosphatase highly expressed in fruit. The sixth gene was the first cytosolic NAD-dependent malate dehydrogenase gene isolated from fruit. Gene expression was studied during the fruit development of two peach cultivars, a normal-acid (Fantasia) and a low-acid (Jalousia) cultivar. The overall expression patterns of the organic acid-related genes appeared strikingly similar for the two cultivars. The genes involved in organic acid metabolism showed a stronger expression in ripening fruit than during the earlier phases of development, but their expression patterns were not necessarily correlated with the changes in organic acid contents. The tonoplast proton pumps showed a biphasic expression pattern more consistent with the patterns of organic acid accumulation, and the tonoplast pyrophosphatases were more highly expressed in the fruit of the low-acid cultivar during the second rapid growth phase of the fruit.

Variability in Sugars, Acids, Firmness, and Color Characteristics of 12 Peach Genotypes

A wide range of color, sugar, and acid composition was found among 12 peach [Prunuspersica (L.) Batsch] genotypes. Among the high-acid genotypes, a trend of increasing Hunter `a' values, fructose, soluble solids concentration (SSC): titratable acidity (TA) ratio, and decreasing TA and citric acid levels was noted with decreasing mesocarp firmness. Mesocarp firmness was correlated with both skin and flesh `a' values within all genotypes. Among genotypes, the Hunter `a'/firmness relationship varied. `Elberta', a cultivar known to retain a greenish ground color, had a lower Hunter `a' value when soft than did more recent releases such as `Dixiland', `Redhaven', and `Suwanee'. `Sam Houston', a low-acid cultivar, had lower TA and malic, citric, and quinic acid levels than the other cultivars. The dominant acid for all genotypes was malic (50% to 60% of total) with about equal amounts of citric and quinic. Soluble sugars included sucrose (54% of total), fructose (31%), and glucose (15%). `Sam Houston' had lower SSC, a higher percentage of sucrose, lower levels of glucose and fructose, but the same relative sweetness values as the high-acid cultivars.