Cindy B. S. Tong

Chilling-induced ethylene production by beans and peas

The effects of chilling on ethylene production by leaf discs and whole plants of bean (chilling-sensitive) and pea (chilling-tolerant) were studied. When pea or bean leaf discs were excised and incubated at 25°C, transient increases in ethylene production and 1-aminocyclopropane-1-carboxylic acid (ACC) accumulation were observed. Both pea and bean discs kept at 5°C evolved little ethylene, but levels of ACC increased in pea discs and not in bean discs. When discs of either species were chilled at 5°C immediately after excision and then transferred to 25°C 9 h later, increases in their ACC levels and ethylene production rates were observed. Discs were also incubated at 25°C for 12 h to allow excision-induced ethylene production to subside and then chilled at 5°C. Nine hours later, these discs were transferred to 25°C, and an increase in ethylene production was observed. These data indicate that chilling suppresses excision-induced ethylene production and enhances the production of ethylene after transfer to 25°C. Chilling of whole plants resulted in increased production of ethylene and ACC in the chilling-sensitive bean but not in the chilling-tolerant pea. Treatment of bean plants with the ethylene antagonists silver thiosulfate, norbornadiene, or aminooxyacetic acid, or of pea plants with ethylene, did not affect the appearance of chilling injury symptoms, indicating that ethylene does not induce injury symptoms and may not have an adaptive role in chilling stress.

Comparison of periderm color and anthocyanins of four red potato varieties

The color, anthocyanin content per given surface area, and phenolics content of tuber periderm of four different varieties of red potatoes were compared. Three of the varieties, Norland, Red Norland, and Dark Red Norland, are members of a color sport family. Freshly harvested ‘Norland’ differed significantly in color, but not anthocyanin content per given surface area, from its sports. ‘Red Norland’ tubers were lighter in color than those of ‘Dark Red Norland’. In general, storage resulted in darkening of tubers and, except for the fourth variety, MN17922, a decrease in anthocyanin content per given surface area. Tubers from green-killed ‘Red Norland’ plants were more purplish-red than those from vine-killed plants. Stored tubers had greater periderm total phenolics content than freshly harvested tubers. The increase in periderm phenolics and decrease in anthocyanin content per given surface area may lead to darkening of tubers with storage. Cell walls connecting periderm to cortex tissue of ‘MN17922’ tubers were thinner than those in ‘Norland’ tubers, which may explain why it is realtively easy to separate the periderm of ‘MN17922’ from its cortex.

Comparison of polyphenol oxidase in tubers of Solanum tuberosum and the non-browning tubers of S. hjertingii

Solarium hjertingii, a wild potato species, does not exhibit enzymatic browning nor blackspot. Blackspot and enzymatic browning are physiological disorders that are caused by the reaction of the enzyme polyphenol oxidase with phenolic substrates, resulting in discoloration of tuber cortex. We determined thatS. hjertingii has a low amount of at least one of the polyphenol oxidases in its tubers compared toS. tuberosum. Less than 5 μg ofS. tuberosum polyphenol oxidase protein, as determined from Western blot staining, had measurable enzymatic activity. In contrast,S. hjertingii protein with comparable staining had no detectable activity.CompendioSolarium hjertingii, una especie silvestre de papa, no presenta el bronceado enzimático ni la mancha negra. La mancha negra y el broncea.do enzimático son desórdenes fisiológicos causados por la reacción de la enzima polifenol oxidasa con los sustratos fenólicos, que dan lugar a la descoloración de la corteza del tubérculo. Nosotros determinamos queS. hjertingii tiene una baja concentración de por lo menos una de las fenol oxidasas en sus tubérculos, en comparación conS. tuberosum. Una cantidad menor de 5μg de la proteína polifenol oxidasa deS. tuberosum, determinada por tinción en Western blot, mostró una actividad enzimática que se podía medir. En contraste, la proteína deS. hjertingii con una tinción semejante no mostró actividad detectable.

Blue Light Inhibition of Tuberization in a Day-Neutral Potato

In tests on the effects of light quality on potato tuberization, continuous blue light was found to consistently inhibit tuberization of tissue-cultured plantlets of Solanum tuberosum ssp. tuberosum cv. ‘Norland’. Other tested cultivars, including sports of ‘Norland’, formed tubers under continuous blue light. Microarrays identified BL, GA7ox, and Nudix genes as exhibiting altered expression in response to blue light treatment. Quantitative RT-PCR (qRT-PCR) showed that GA7ox RNA increased in ‘Norland’ but not in ‘Sangre’ plantlets in blue light compared to darkness. RNA levels of genes identified in the literature as having roles in potato tuberization were also measured using qRT-PCR. Levels of GA20o1x, but not GA2ox, RNA increased in response to blue light in ‘Norland’ plantlets. BEL5 RNA content was greater under blue light compared to darkness for both ‘Norland’ and ‘Sangre’ plants. Levels of FT were not significantly different in blue light compared to dark-treated ‘Norland’ plants, but were low in blue light-treated compared to dark-treated ‘Sangre’ plants. Addition of ancymidol to ‘Norland’ plants exposed to blue light overcame blue light inhibition of tuberization. Ancymidol prevents the oxidation of ent-kaurene to ent-kaurenoic acid, thus inhibiting gibberellin biosynthesis. These data suggest that blue light may increase GA accumulation in ‘Norland’ plants, as has been shown to occur in Arabidopsis plants. The novel effect of blue light in inhibiting tuberization of ‘Norland’ plants suggests that this system could be a useful tool in further elucidating the mechanisms of day-neutral potato tuberization.

Using mixed-effects models to estimate the effect of harvest date and its interactions with post-harvest storage regime on apple fruit firmness

Summary The effects of harvest date and storage on apple (Malus pumila Mill.) fruit firmness have been studied using numerous cultivars. Many factors, such as cultivar, year, orchard location, and storage condition appear to confound the effects of harvest date, making it difficult to predict how firmness would change over time. Firmness in ‘Minneiska’ fruit, a cross between ‘Honeycrisp’ and ‘Minnewashta’, was measured over several harvests at multiple locations in three States over 2 years, with harvests occurring over 3 – 4 weeks in each year. Linear mixed-effects models were used to isolate the effects of year, orchard, storage duration, and storage conditions on harvest date effects on firmness. The models indicated that harvest date had little effect on fruit firmness at harvest, regardless of orchard location, and the variance due to year was small. Storage had a large effect on firmness, but the differences between air storage and controlled atmosphere storage were not significant. Simulations were performed to determine the effect of sample size on fixed effect estimates, especially harvest date. The results of these simulations suggested that increasing the sample number beyond ten fruit per treatment had little impact on the estimates.

Cloning and accumulation of anthocyanin biosynthesis genes in developing tubers

Anthocyanins are a class of flavonoids that are responsible for the pigmentation of red potato periderm. The cDNAs of two genes were cloned from ‘Norland’ periderm and, based on their sequence similarity to genes in various databases, were identified as the anthocyanin biosynthetic genes for leucoanthocyanidin dioxygenase (EC 1.14.11.19) and UDP glucose: flavonoid 3-O-glucosyl transferase (EC 2.4.1.91). The mRNA accumulation of these genes in periderm during the development of tubers was determined using RNA gel blot analyses. The mRNA of the putativeLDOX was detected in cortex tissue and microtubers, but not in periderm. While mRNA of the putativeUFGT was detected in cortex tissue and periderm of young tubers, but not in periderm of tubers weighing more than 25 g. These data suggest that accumulation ofLDOX andUFGT mRNA may limit anthocyanin synthesis as Norland tubers develop.ResumenLas antocianinas son una clase de flavonoides responsables de la pigmentación roja del peridermo del tubérculo de papa. Se clonaron los cDNAs de dos genes del peridermo de ‘Norland’ y en base a la semejanza de sus secuencias con los genes de varias bases de datos, fueron identificados como los genes que sintetizan las antocianinas leucoantocianidina dioxigenasa (EC 1.14.11.19) y de la UDP glucosa: flavonoide 3-O-glucosil transferasa (EC 2.4.1.91). La acumulación de mRNA de estos genes en el peridermo, durante el desarrollo de los tubérculos fue determinada utilizando el análisis gel blot. El mRNA delLDOX putativo fue detectado en el tejido de la corteza y los microtubérculos, pero no en el peridermo, mientras que el mRNA delUFGT putativo fue detectado en el tejido de la corteza de tubérculos jóvenes, pero no el peridermo de tubérculos con un peso mayor a los 25g. Estos datos sugieren que la acumulación deLDOX yUFGT mRNA pueden limitar la síntesis de antocianina a medida que los tubérculos de Norland desarrollan.

Two QTL characterized for soft scald and soggy breakdown in apple (Malus × domestica) through pedigree-based analysis of a large population of interconnected families

Soft scald and soggy breakdown are important postharvest physiological disorders of apple (Malus × domestica). ‘Honeycrisp’ and some of its offspring are particularly susceptible to developing these disorders. The purpose of this study was to identify molecular markers associated with high incidences of soft scald and soggy breakdown for use in marker-assisted breeding. Towards this aim, we employed a pedigree-based approach using mostly germplasm related to ‘Honeycrisp.’ Two quantitative trait loci (QTL) were consistently identified on linkage groups (LGs) 2 and 16 across the 2014 and 2015 harvest years. The same QTL were identified for both storage disorders, indicating that they may be physiologically related. ‘Honeycrisp’ is homozygous for an identical by state haplotype at the LG2 QTL that was consistently associated with a deleterious effect on soft scald and soggy breakdown incidence. This haplotype was traced through SNP-confirmed pedigrees to the following cultivars: ‘Grimes Golden,’ ‘Northern Spy,’ ‘Rome Beauty,’ and ‘Fireside’ and is common in derived apple germplasm. Haplotypes at the LG16 QTL could not be adequately characterized due to variation between years combined with effects of this QTL being of relatively smaller size and being most evident in individuals that carry two copies of the deleterious haplotype at the LG2 QTL. These results suggest that limiting homozygosity of the deleterious haplotype at the LG2 QTL through marker-assisted breeding would be a valid strategy to limit soft scald and soggy breakdown incidences in apple seedling populations.

Factors influencing the Salmonella internalization into seedpods and whole plants of Arachis hypogaea (L.)

Here we investigated whether Salmonella enterica serovar Typhimurium ATCC 14028 was capable of internalizing in peanut seedpods and plants when exposed to inoculated soil and the edaphic factors that influenced uptake. Intact dry Virginia (DV) and fresh green Virginia (GV) seedpods were exposed to soil containing 6.5 Log (CFU/g) Salmonella under different soil moisture conditions. Internalization of S. Typhimurium into peanut plants germinated in inoculated soil was also examined with and without Bradyrhizobium (Arachis) sp.NC92. Salmonella counts recovered from GV seedpods were on average of 2.0 Log (CFU/pod) less than those recovered from DV seedpods. The internalization in DV pods was only observed at soil water content of 15% or greater in a loamy sand soil. S. Typhimurium was detected inside peanut plant tissues during most testing times. Cells were recovered from stem samples (3.5 Log CFU/g) at greater levels than it was observed for root (2.6 Log CFU/g) and leaf (1.7 Log CFU/g) samples. Overall, recovery of Salmonella from stem, root, and leaf samples were lower when B. NC92 was inoculated on seeds before sowing, but this trend was not significant. Our observations suggest possible routes of contamination of Salmonella into peanut products from soil.

Differential Accumulation and Degradation Of Anthocyanins In Red Norland Periderm is Dependent On Soil Type And Tuber Storage Duration

To determine how soil type, 2,4-dichlorophenoxyacetic acid (2,4-D) treatment, and storage affects color and anthocyanin accumulation of Red Norland potatoes, tubers were grown in sand or peat, with or without 2,4-D treatment, and measured at vine kill, harvest or after storage. Tubers grown in sand were less red and accumulated fewer anthocyanins than tubers grown in peat. 2,4-D treatment increased redness regardless of soil type. Redness loss varied greatly among tubers with storage. Tubers that lost color with storage had a two-fold reduction in anthocyanins, and a two-fold increase in benzoic and cinnamic acids compared to harvest, indicating chemical degradation of anthocyanidins via B-ring cleavage and autoxidation. Sand-grown potatoes did not exhibit greater cinnamic acids compared to peat-grown potatoes, suggesting that their color differences were due more to differences in biosynthesis than degradation during skin set. To improve Red Norland tuber color, research should focus on increasing biosynthesis of anthocyanins.ResumenPara determinar la influencia del tipo de suelo, el tratamiento con el ácido 2,4-diclorofenoxiacético (2,4-D) y el almacenamiento, sobre el color y acumulación de antocianinas en papa Red Norland, se sembraron tubérculos en arena o turba, con o sin tratamiento con 2,4-D, con mediciones al secado del follaje, a la cosecha, o después del almacenamiento. Los tubérculos que crecieron en la arena eran menos rojos y acumularon menos antocianinas que los cultivados en turba. El tratamiento con 2,4-D aumentó lo rojizo independientemente del tipo de suelo. La pérdida de la pigmentación roja varió grandemente entre los tubérculos con almacenamiento. Los tubérculos que perdieron el color en el almacén tuvieron el doble de reducción en antocianinas y un aumento al doble en ácidos benzoico y cinámico comparados a la cosecha, indicando degradación química de antocianidinas por vía del rompimiento del anillo B y por autooxidación. Las papas cultivadas en la arena no exhibieron mayores ácidos cinámicos en comparación con las cultivadas en la turba, lo que sugiere que sus diferencias en color se debieron más a diferencias en la biosíntesis que a la degradación durante el embarnecimiento de la piel. Para mejorar el color del tubérculo en Red Norland, la investigación debería enfocarse en el aumento de la biosíntesis de antocianinas.

Tomatillo Resistance to Colorado Potato Beetle (Coleoptera: Chrysomelidae)

Tomatillo (Physalis ixocarpa Brot ex Hornem) resistance to the Colorado potato beetle, Leptinotarsa decemlineata (Say), was evaluated in the laboratory. In vivo assays confirmed that L. decemlineat...