`Oroblanco' is an early-maturing pummelo-grapefruit hybrid (Citrus grandis × C. paradisi). The fruit of this cultivar are usually picked in October and are marketed while their peel color is still green. However, during long-term storage, the fruit turns yellow, and loses much of their commercial value. In a previous study, we found that application of gibberellic acid and low storage temperatures of 2 °C (35.6 °F) markedly reduced the rate of degreening. However, `Oroblanco' fruit are sensitive to chilling injuries, and thus could not be stored at 2 °C for long periods. In the present study, we examined the possible application of intermittent warming (IW) and temperature conditioning (TC) treatments, in order to retain the green fruit color during long-term cold storage but without enhancing the development of chilling injuries. It was found, that following storage at 2 °C, either with or without IW and TC, the fruit retained green color up to 16 weeks, whereas at 11 °C (51.8 °F) fruit turned yellow after 8 weeks. However, untreated fruit held continuously at 2 °C developed 40, 51, and 68% chilling injuries after 8, 12, and 16 weeks, respectively. IW (storage at cycles of 3 weeks at 2 °C + 1 week at 11 °C) reduced the amount of chilling injuries to only 5, 7 and 11% after the same periods of time, respectively. TC [a pre-storage treatment for 7 days at 16 °C (60.8 °F) before continuous storage at 2 °C] effectively reduced the development of chilling injuries to only 5% after 8 weeks of storage, but was ineffective in reducing chilling damage after longer storage periods. Because chilling damaged fruit is prone to decay, the IW and TC treatments also reduced the incidence of decay development during storage. The IW and TC treatments did not affect juice total soluble solids and acid percentages, but did affect fruit taste and the amounts of off-flavor volatiles emitted from the juice. Taste panels indicated that the taste score of untreated control fruit stored at 11 °C gradually decreased during long-term storage, and that this decrease was more severe in chilling damaged fruit stored continuously at 2 °C. The taste of IW-treated fruit remained acceptable even after 16 weeks of storage, and TC-treated fruit remained acceptable for up to 12 weeks. Fruit taste scores were inversely correlated with the concentrations of ethanol and acetaldehyde detected in the juice headspace.
R. Porat, B. Weiss, L. Cohen, A. Daus, and E. Cohen
E. Tanne, L. Kuznetsova, J. Cohen, S. Alexandrova, and A. Gera
Recently, yellows diseases have become more common in Israel, and phytoplasmas have been detected in some of these diseased crops. Commercial fields of two celosia species (Celosia plumosa L. and C. cristata L.) also have exhibited yellows symptoms and total crop failure. Typical mycoplasma-like bodies were observed in infected but not in healthy plants. The same plants were analyzed for the presence of phytoplasma by polymerase chain reaction (PCR), using the universal oligonucleotide pair r16SF2/r16SR2, followed by nested PCR using group-specific primers. Restriction analyses performed with these products indicated that two different types of phytoplasmas are infecting celosia. PCR-RFLP analysis of one type revealed a restriction pattern typical of aster yellows. Similar analysis of the second type indicated possible relatedness, though not identity, to the pattern of phytoplasmas of the Western-X group. This is, to our knowledge, the first report of phytoplasma infection in celosia.
Charles L. Rohwer, Lynette Y. Wong, David C. Zlesak, and Jerry D. Cohen
It may seem paradoxical that a teaching assistant (TA), whose involvement in a particular class may be limited to a single semester, can provide continuity in the classroom from year to year. Improvement in TA performance from one year to the next also seems difficult to achieve under such circumstances. However, when TAs are encouraged to document classroom activities, specific TA responsibilities, and student concerns, this documentation may be useful in achieving continuity, improved TA performance, and result in a better classroom experience for the students. In addition to the benefit of documentation, TAs, in conjunction with faculty, can together reflect upon how well the objectives of specific laboratories were met. TAs can contribute to generating and documenting ideas that may be implemented to help improve student learning in the future. Each TA comes to the course with a unique collection of horticultural and teaching experiences and has the potential to aid faculty in course refinement and improvement. We explain how TA-directed documentation can provide continuity and year-to-year improvement in horticulture classrooms using our experience with HORT 3005, a required plant physiology laboratory course specifically targeted to horticulture students at the University of Minnesota.
Veronica L. Justen, Jerry D. Cohen, Gary Gardner, and Vincent A. Fritz
Glucosinolates (GSLs) are thioglucosides with important properties for plant defense and human health. The objective of this study was to quantify yield and GSL concentration in turnip (Brassica rapa subsp. rapa) roots and shoots as influenced by colored plastic mulches. Four turnip cultivars (‘Just Right’, ‘Purple Top’, ‘Royal Crown’, and ‘Scarlet Queen’) were grown over five mulch treatments: white, yellow, silver, red, blue, and a bare soil control in both a May and an August planting in 2006 and 2007. Yield varied by variety; however, there was no consistent relationship between mulch treatment and yield. Glucosinolate concentrations and profiles varied with tissue type, genotype, and environmental factors, including temperature and planting date. Mulch-dependent increases in GSL concentrations were not consistent across tissue types, cultivars, planting dates, and years of the study, possibly as a result of differences in climatic factors and mulch-dependent changes in soil temperature between planting dates and years of the study.