Sourcing Blue Mold Rot on Bulbs
Research conducted at the University of Denmark aimed to clarify the causal agents of “blue mold rot” in vegetable and flower bulbs. Penicillium corymbiferum is the fungus most often cited as the cause of blue mold rot. This assessment is too generalized since the species P. corymbiferum has recently been subdivided into seven taxa. In this study, the various Corymbifera taxa were evaluated in Allium sativum, A. cepa (yellow onion), A. cepa (red onion), Tulipa gesneriana and Gladiolus sp.. Flower bulb infection usually results in reduced root growth and an increased rate of floral abortion.
The leaf epidermis and root disk region of undamaged bulbs were inoculated with fungal spore suspensions. After a three-week incubation, the bulbs were inspected for symptoms of infection. Infections naturally occur at a wound in the epidermis or a crack in the basal plate at the site of root emergence. Brown discoloration of the root initials and eventual rot of internal meristematic tissue are the symptoms associated with infection.
Inoculation with P. hirsutum and P. tulipae produced the worst infection symptoms in tulip. The basal root plate was more affected than the leaf epidermis, though discoloration of the leaf initials was an observed symptom. Though P. albocoremium, P. hordei, P. radicicola and P. venetum produced infection symptoms, they were less pronounced, and P. allii did not produce any symptoms in tulip.
Gladiolus corms were infected by P. hirsutum, P. venetum and P. tulipae. The root plate did not allow fungal growth as it was lignified; however, the wounding sites in the epidermis did produce infection symptoms. At these sites, infections were moderate to severe with internal cavity formation and discolored tissue reaching the center of the corm.
The primary concerns for the need to correctly identify these sources of blue mold rot are to eliminate crop loss and recognize the danger posed to consumers by the fungal production of a neurotoxin that has been implicated in tremorgenic toxicosis in dogs.
Overy, D.P., J.C. Frisvad, U. Steinmeier, and U. Thrane. 2005. Clarification of the agents causing blue mold storage rot upon various flower and vegetable bulbs: implications for mycotoxin contamination. Postharvest Biology and Technology 35:217-221.
Effect of Photoperiod and Sowing
Time on Lupinus varius L.
Lupinus varius is a short to medium, softly hairy annual with inflorescences on the main stem and branches with blue flowers that are longer than some related species now used in the cut flower industry. Researchers at Akdeniz University in Turkey have evaluated the effect of photoperiod and sowing time on the growth and flowering characteristics to determine the market potential for this native flower.
The seeds were collected from a native population and were mechanically scarified prior to sowing to overcome impermeable seed coat dormancy. The plants were grown in an unheated plastic greenhouse in Antalya, Turkey. The loam soil was solarized prior to each growing season and had a pH of 7.4. Photoperiod treatments consisted of natural, 14- and 16-hour day-lengths. Sow dates were September 28, October 28 and November 28. As the plants matured, numerous flowering characteristics were observed, recorded and analyzed.
They found that photoperiodic lighting (16-hour day-length) shortened the days to flower by 10-15 days and increased plant height in all sowing times compared to natural days. Delayed sowing resulted in decreased days to flower and reduced plant height under all daylengths. There was no significant difference between natural days and 16-hour daylength treatments for stem and branch inflorescence diameters, lengths of branch, main and branch inflorescences. Delayed sowings resulted in a linear decrease in those flowering characteristics under all daylength treatments.
Plants sown in September in an unheated greenhouse under Mediterranean coastal climate conditions produced a main inflorescence averaging 21 in (53 cm), with 52 flowers. Each plant had four branches 27.5 in (70 cm) in length with the inflorescence measuring 10.5 in (27 cm) and displaying 33 flowers per inflorescence. It could also be easily grown in February under the same conditions. Culturally Lupinus varius is promising as a new cut flower species; however, further investigation of adaptability to growing conditions and post-harvest requirements are needed.
Karaguzel, O., I. Baktir, S. Cakmakei, V. Ortacesme, B. Aydinoglu, and M. Atik. 2005. Responses of native Lupinus varius (L.) to culture conditions: effects of photoperiod and sowing time on growth and flowering characteristics. Scientia Horticulturae 103:339-349.
A Closer Look ar Gravistimulation
The widely accepted theory describing the physiological response that leads to gravitropic stem bending is perhaps oversimplified. In short, the theory suggests that an auxin gradient with elevated levels of auxin on the lower side is generated across the stem resulting in asymmetrical growth and a visually noticeable upward bending response. Plant scientists in Israel have put forth evidence that the gravitropic bending is a result of a complex multi-step response and continue working to identify the cellular components and signaling mechanisms responsible.
In this study, Ornithogalum cut flowers with two to four open florets were treated with a 20-22 hour pulse of distilled water, or one of five solutions containing a calcium modulator. They underwent simulated air transport and laboratory conditions. The curvature resulting from gravistimulation was measured and the postharvest flower quality was evaluated.
Under dry transport conditions, the calcium chelator EGTA most effectively inhibited stem bending. Under wet laboratory conditions, all calcium chelators tested (EDTA, CDTA, EGTA) and the calcium channel blocker LaCl3 similarly inhibited stem bending. No obvious damage to the flowering stalks was observed and the vertical spike growth was not affected, implying the calcium antagonists do not directly damage the spike, but affect a response mechanism.
This study also found that spikes placed horizontally developed a gradient of ethylene production rates across the bending stem, favoring the lower stem flank. Both EGTA and CDTA treatments directly influenced ethylene production, ultimately abolishing the formation of the ethylene production gradient across the stem. The results of this study are consistent with the results of previous similar studies conducted on snapdragons. As gravistimulation is further understood, the deleterious affects may be overcome with postharvest treatment.
Friedman, H., S. Meir, I. Rosenberger, A.H. Halevy, S. Philosoph-Hadas. 2005. Calcium antagonists inhibit bending and differential ethylene production of gravistimulated Ornithogalum ‘Nova’ cut flower spikes. Postharvest Biology and Technology (In Press).
Sourcing Blue Mold Rot on Bulbs