Bill B. Dean

Blackspot pigment development of resistant and susceptibleSolanum Tuberosum L. genotypes at harvest and during storage measured by three methods of evaluation

Blackspot pigment development was measured by three methods: 1) impact, 2) abrasive peeling, and 3) oxidation of tuber homogenates. Genotypes and storage periods were used as variable treatments. All methods were able to separate genotypes based on blackspot resistance although the abrasive peel and homogenization methods provided more consistent results than the impact bruise method. Bruise resistant genotypes transferred their resistance to progeny in crosses with a susceptible genotype which was correlated with tyrosine content. According to the traditional impact bruise technique, tuber resistance to blackspot increased during the eight-to ninemonth storage at 3 C. In contrast, resistance was found to decrease with the homogenization procedure and did not change with the abrasive peel technique. Free tyrosine was consistently associated with blackspot pigment development but chlorogenic acid and caffeic acid were not.CompendioSe midió el desarrollo del pigmento de la mancha negra por tres métodos: 1) impacto, 2) pelado con abrasivos y 3) oxidation de homogenados de tubérculo. Se utilizaron a los genotipos y periodos de almacenamiento como tratamiento variables. Todos los métodos permitieron separar a los genotipos basándose en la resistencia a la mancha negra aunque el pelado con abrasivos y los métodos de homogenización proveyeron resultados más consistentes que el método de magulladuras al impacto. Los genotipos resistentes a las magulladuras transfirieron esta resistencia a sus progenies en cruzamientos con un genotipo susceptible que estaba correlacionado con el contenido de tiroxina. De acuerdo con la técnica tradicional de magulladuras al impacto, la resistencia de los tubérculos a la mancha negra se incrementó durante los ocho a nueve meses de almacenamiento a 3 C. Por el contrario, la resistencia disminuyó con el procedimiento de homogenización y se mantuvo estable con la técnica de pelado con abrasivos. La tiroxina libre estuvo consistentemente asociada con el desarrollo de la pigmentation de la mancha negra, pero los ácidos clorogénico y cafeínico no mostraron tal asociación.

Differences in free and protein-bound tyrosine among potato genotypes and the relationship to internal blackspot resistance

Twelve potato clones were selected to represent the full range of internal blackspot response in order to determine the relationships between tuber protein, free tyrosine, and blackspot susceptibility. The blackspot reaction for each clone was consistent over five growing seasons, including tubers grown over a normal season (mature), and short season (immature) during one year. The blackspot index, determined by either an abrasive peel test or an impact bruise test, was highly correlated with the tyrosine content of the tubers (r = 0.90 p = 0.001 for the means of each clone over five location-years). Tubers with free tyrosine levels below 4 μmole/g dry weight consistently showed a resistant blackspot response. The relationship between tyrosine and blackspot susceptibility was also found in stolon and bud ends from five of the clones which represented the extremes of blackspot reaction and genetic diversity. Bud end samples of each of the clones had lower tyrosine content and a corresponding reduction in blackspot compared with stolon ends. Phenols, other than tyrosine, showed no consistent relationship to the blackspot reaction.There was a very high negative correlation between free tyrosine and estimated protein-bound tyrosine. R values ranged from −0.85 to −0.97 (p = 0.001) for mature tubers of the 12 clones over 4 growing seasons. Total tyrosine (free, plus protein-bound) remained relatively constant. There were no significant differences in mean total tyrosine content among the 12 clones over five location-years of testing; and there were no significant differences among the five growing seasons except for the short season (immature) tubers which were 14% lower in total tyrosine content. These results indicate a remarkably constant level of total tyrosine production in the twelve clones studied, that represented diverse genetic backgrounds. Mature tubers of all genotypes contained 26 ± 1 μmole/g dry weight total tyrosine. Partitioning of tyrosine between tuber protein and the free amino acid pool varied with genotype and appeared to be a major determinate of blackspot resistance.CompendioSe seleccionaron doce clones de papa para representar el rango completo de la respuesta de la mancha negra interna para determinar la relación entre la proteína, la tiroxina libre y la susceptibilidad a la mancha negra. La reacción a la mancha negra para cada clon fue consistente durante cinco temporadas, incluyendo tubérculos que crecieron en una temporada normal (maduros) y en una temporada corta (inmaduros) durante un año. El índice de mancha negra, determinado ya sea por una prueba de peladura con abrasivo o por una prueba de daño por impacto, estuvo ampliamente correlacionado con el contenido de tiroxina de los tubérculos (r=0, 90 p = 0,001 para los promedios de cada clon en cinco anos-localidad). Los tubérculos con niveles por debajo de 4 μmole/g de peso seco mostraron consistentemente una respuesta resistente a la mancha negra. La relación entre la tiroxina y la susceptibilidad a la mancha negra también fue encontrada en los estolones y puntas de las yemas de cinco de los clones que representaron los extremos de la rección a la mancha negra y diversidad genética. Muestras de las puntas de las yemas de cada uno de los clones tuvieron contenidos más bajos de tiroxina y la reducción correspondiente en mancha negra en comparación con las puntas de los estolones. Otros fenoles diferentes a la tiroxina no mostraron una relación consistente a la reacción a la mancha negra.Hubo una correlación negativa muy alta entre la tiroxina libre y el estimado de tiroxina ligada a proteína. Los valores de R variaron de −0,85 a −0.97 (p=0,001) para los tubérculos maduros de los 12 clones durante cuatro temporadas. La tiroxina total (libre, más ligada a proteína) permanecieron relativamente constantes. No hubieron diferencias significativas en el contenido promedio de tiroxina total entre los 12 clones durante cinco de los años-localidad y tampoco las hubo entre las cinco temporadas excepto para los tubérculos de la temporada corta (inmaduros) que tuvieron 14% menos de contenido total de tiroxina. Estos resultados indican un nivel constante notable de producción de tiroxina total en los doce clones estudiados y que representaban bases genéticas diversas. Los tubérculos maduros de todos los genotipos contuvieron 26 ± 1 μmole/g de peso seco de tiroxina total. La distribución de la tiroxina entre la proteína del tubérculo y el (pool) de amino ácidos libres varió con el genotipo y pareció ser un factor determinante de la resistencia a la mancha negra.

Effect of Nectar Composition and Nectar Concentration on Honey Bee (Hymenoptera: Apidae) Visitations to Hybrid Onion Flowers

Abstract Floral nectar characteristics of nine inbred lines of onion (Allium cepa L.) were examined to determine their influence on the attractiveness of the onion flowers to honey bees (Apis mellifera L.). Potassium concentrations and sugar concentrations of the nectar did not significantly correlate with the number of bee visits received by an umbel. The average amount of nectar produced by both the umbels and the individual florets was significantly positively correlated with the number of bee visits. Our results suggest that selection for flowers with high nectar production may lead to a higher rate of pollination of the onion seed crop.

Harvesting potatoes with minimum damage

Temperature, tuber condition and harvester operation must be considered if potatoes are to be harvested with minimum damage. In general, total damage increased as temperature decreased; however, the type of damage resulting from impact was influenced by temperature and tuber condition. The data indicate that a tuber turgidity level occurs wherein total damage susceptibility level is minimal for a given tuber temperature and that the proper tuber turgidity level changes as temperature changes. A tuber hydration level which produces little damage when bruised at a flesh temperature of 65–70 F results in severe damage (shatter bruise) when subjected to the same force at 45–50 F. Conversely, a hydration level which results in severe blackspot at 65–70 F may result in slight to moderate total damage when subjected to the same impact at 50–55 F.Data from several commercial harvester studies indicate that damage may increase rather than decrease with a reduction of harvester speed. The ratio of chain speeds to forward speed was found to be more important than forward speed alone. The optimum ratios varied and were dependent on potato yield. Theoretical ratios based on the volume of tubers at different yield levels and harvester chain capacities were calculated and compared with actual ratios of commercial harvest operation. Harvesters operated with chain speed to forward speed ratios near the theoretical ratios resulted in low tuber damage (25%) with forward speed ranges of 1.60 to 3.25 mph. Harvesters operating with ratios differing considerably from theoretical ratios resulted in a high level of damage (66%).The catechol test identified shatter bruise damage which ruptured the skin, but did not detect internal blackspot. Therefore, the catechol test should be used with discretion when attempting to determine the total damage level. Lye peeling and abrasive peeling identified both blackspot and severe shatter bruise damage and should be used when determining harvester operation speeds when both types of damage occur.

The Effect of Potassium Deficiency on Chemical, Biochemical and Physical Factors Commonly Associated with Blackspot Development in Potato Tubers

Blackspot bruise is a physiological disorder of potato tubers resulting from mechanical damage to tissues during handling. This study examined the effect of potassium nutrition on biochemical and physical changes normally associated with blackspot bruise in potato tubers. Four potato (Solanum tuberosum L.) genotypes (TXA 763-5 [very resistant], Ranger Russet [very susceptible], Russet Burbank [susceptible], and Lemhi Russet [very susceptible]) differing in susceptibility to blackspot bruise were grown at three potassium nutrition levels (100%, 10% and 0% of the potassium in full strength Hoagland’s solution). Tubers from the three treatments were tested for their chemical, biochemical and physical characteristics commonly related to blackspot bruise susceptibility. The potential to develop malanin pigments was measured as total oxidative potential (optical density, OD475) of clarified tuber homogenates. Tuber tissue extracts were assayed for polyphenol oxidase (PPO) activity with catechol, measured as increase in OD410 over time. Specific gravity of tubers was determined with a brine solution series. Physical property measurements were made by impacting cores of tuber tissue in a specially designed instrumented pendulum. Shock wave speed, Young’s modulus, failure stress, and failure strain were all measured dynamically during impact. Tubers produced under both the 10% and 0% potassium regimens had almost 2x the free tyrosine of control tubers. The 0% potassium tubers had significantly higher PPO activity than the control. Both of these factors likely contributed to the significantly higher total oxidative potential that was observed in tubers from both the 10% and 0% potassium treatments. Tubers from both the 0% and 10% potassium treatments had a significantly lower Young’s modulus (a measure of stiffness), significantly lower failure stress and the shock wave of impact propagated through both of them significantly slower. Although the cultivars were significantly different in their susceptibility to black pigment development, they all responded similarly to the treatment with regards to the variables measured. The TXA-763-5 clone was much more susceptible to developing black pigments in these tests than expected. The other three cultivars performed as they do in commerce.

Genetic characterization of reduced melanin formation in tuber tissue ofSolatium hjertingii and hybrids with cultivated diploids

The degree of enzymatic browning in tubers was examined quantitatively in five plant introduction (PI) accessions ofSolanum hjertingii and in hybrids of this species with cultivated diploids that had high enzymatic browning. Polyphenol oxidase activity and melanin formation inS. hjertingii accessions was subjected to an analysis of variance. There was significant variation in melanin formation within accessions but the between accession component was not significant. This indicates that it would be most advantageous to select low melanin formation by evaluating individual genotypes within an accession. Significant variation for PPO activity existed between accessions, indicating that selection on the basis of accession means would be the best means of selecting for lower PPO activity. Both parameters were much lower in allS. hjertingii genotypes compared to tetraploid cultivars known for their susceptibility to internal blackspot when mechanically damaged. The reduced browning inS. hjertingii was due to a lack of PPO activity and not the shortage of substrate. Progenies, and parents of four crosses between selectedS. hjertingii genotypes and cultivated diploids were measured for PPO activity and melanin formation. The mean performance of the progenies was closest to theS. hjertingii parent in all cases. Degree of dominance indicated nearly complete dominance or overdominance in the direction of theS. hjertingii parent. These results are discussed in light of other work which indicates that protein antigenic to PPO antibody is present inS. hjertingii. It appears that inactive PPO is present in the tubers. The pronounced dominance of low PPO activity and suppression of melanin formation in the hybrids withS. hjertingii is promising for the utility of this wild species as a source of genetic factors that, upon introgression into the cultivated potato gene pool, would suppress browning.

Introgression of the low browning trait from the wild Mexican species Solanum hjertingii into cultivated potato (S. tuberosum L.)

Internal discoloration of tubers resulting from impact damage (blackspot bruise) is a serious quality problem in potato production and utilization, reducing profits to growers and increasing costs for processors. Resistance to blackspot bruise has been identified in the wild species Solanum hjertingii and is therefore a potential germplasm resource for genetic resistance to this problem. A bridging cross between S. hjertingii and a cultivated diploid clone was used to produce a triploid hybrid population that exhibited very low tuber browning potential, indicating a dominant pattern of inheritance for this trait. The triploid progeny were subjected to in vitrochromosome doubling and the resulting hexaploid clones were screened for browning potential. A hexaploid clone selected for low browning was reciprocally crossed with cultivated S. tuberosum cultivars exhibiting high susceptibility to blackspot bruise. Tubers obtained from the seed progeny of these 4x-6x crosses (hereafter referred to as the BC1 populations) were evaluated for browning potential and polyphenol oxidase (PPO) activity. Tubers from the BC1 populations displayed a very low potential for melanin production, while PPO activity was quite variable. The low Pearson correlation coefficient (r2 = 0.45), between browning potential and PPO activity suggests that the mechanism of blackspot bruise resistance derived from S. hjertingii cannot be explained simply as a reduction in the initial PPO activity. The expression of substantial resistance to browning and dominant expression pattern in these BC1 progeny indicate that utilizing genetic elements derived from S. hjertingii provides a robust approach for developing blackspot bruise resistant potato varieties.

Tyrosine synthesis in potato tuber tissue from blackspot-susceptible and resistant genotypes

SummaryRadioactively-labeled shikimic acid (14C) was incubated with potato tuber tissue disks to determine the relative rate of tyrosine synthesis in blackspot-resistant and susceptible cultivars. Tyrosine synthesis was 55% higher in the susceptible cultivar, Lemhi Russet, than the resistant clone TXA 763-5. The susceptible clone also partitioned a lower percentage of14C tyrosine into soluble protein than did the resistant genotype. The percentage of labeled free tyrosine which would be available for oxidation by polyphenyloxidase was therefore much higher in the susceptible cultivar.

Effect of cold storage on proteinase and chorismate mutase activities inSolanum tuberosum L. Genotypes differing in blackspot susceptibility

Potato tubers (Solanum tuberosum) from genotypes differing in chemical susceptibility to the physiological disorder blackspot bruise (TXA 763-5, Atlantic, Ranger Russet, Russet Burbank, and Lemhi Russet) were stored for eight months at 3 C. Protein extracts from each cultivar were assayed for proteinase and chorismate mutase (CM) activities. During cold storage, three of five genotypes tested increased in their ability to develop melanintype pigments responsible for blackspot. Concurrent with this were increases in either endopeptidase, aminopeptidase, or CM activities or combinations of enzyme activities specific to genotypes. These increases in enzyme activity may be responsible for the increase in levels of the melanin precursor tyrosine, associated with cold storage of potato tubers.CompendioTuberculos de papa (Solarium tuberosum) que provienen de genotipos que difieren en la susceptibilidad química a la enfermedad fisiológica de la mancha negra causada por golpes (TXA 763-5, Atlantic, Ranger Russet, Russet Burbank y Lemhi Russet) fueron almacenados durante ocho meses a 3 C. Los extractos de proteínas de cada cultivar fueron sometidos a las pruebas de actividad de la proteinasa y chorismata mutasa (CM). Durante el almacenamiento en frío, tres de los cinco genotipos probados aumentaron su habilidad para desarrollar pigmentos del tipo de la melanina, que son los responsables de la mancha negra no infecciosa. Concurrente con ello hubo un incremento en las actividades de la endopeptidasa, aminopeptidasa o CM, o en las combinaciones de las actividades enzimáticas específicas de los genotipos. Estos incrementos en la actividad enzimática, asociados con el almacenamiento en frío de los tubérculos de papa, pueden ser responsables del aumento de los niveles de la tirosina precursora de la melanina.