Laboratory Report

Red and Green Aphids

Essential pigments called carotenoids are beneficial to animal health. Humans commonly take in carotenoids by eating tomatoes, carrots, and other colorful plants. The pea aphid (Acyrthosiphon pisum) is the only known animal species able to produce its own carotenoid molecules. Scientists believe a rare event of gene snitching from a fungus millions of years ago gave the aphid the ability to produce its own carotenoid pigment. Gene transfer across kingdoms, especially from the fungus to the animal kingdom is believed to be extremely uncommon. Body color in the pea aphid is controlled by one gene; if the gene is present in the aphid, a red color is produced and it is a dominant trait. Both red and green forms of the aphid exist in nature, with an ecological impact as a result. Red forms are preferred food sources for predator insects such as ladybird beetles, whereas green forms are preferred oviposition sites for parasitoid wasps. This phenomenon is even more interesting: it was found recently that, amongst aphids containing the gene for carotenoid production, some aphids were green and some were red. In this case, the green aphids were infected with a bacterium (Rickettsiella) resulting in production of substances that masked the red color causing the aphids to be green. Infection by the bacterium is not harmful to the aphid, and may actually help it adapt to certain environmental conditions.

            Science, 19 November 2010 330 (6007): 1102-1104

Targeting Pesky Algae

All photosynthetic organisms require the essential amino acid lysine and are able to synthesize it themselves. Researchers at the Rochester Institute of Technology have looked closely at the pathways photosynthetic organisms follow to synthesize lysine. In an alga (Chlamydomonas reinhardtii), a specific enzyme has been singled out that is common to the various pathways toward lysine synthesis. Using the technique of x-ray crystallography, researchers were able to determine the 3-D structure of the enzyme. This information aids in finding appropriate substances that will perfectly fit into the enzyme molecule and disrupt its function. Since this lysine synthesis enzyme is specific to the alga, products used to disrupt the alga will do no harm to other plants or animals.

            https://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0020439

“Drought” Stress During Wet Winters

Old growth conifers in the Pacific Northwest were found to suffer from impaired water conductivity to their upper branches during certain conditions in winter when water was plentifully available in the root zone. The reason is the formation and accumulation of embolisms in the xylem during freeze-thaw cycles. During a typical summer of heat and dryness, when it would seem logical that the trees would suffer from drought stress, the trees close their stomata and lower their rate of growth. They get through those summer periods better able to conduct what water there is without embolisms. As climate changes, it is not yet well understood whether the Pacific Northwest will experience a consistently warmer, drier climate or a climate with more freeze-thaw cycles.

            American Journal of Botany, June 2011 98 (6): 1007-1015

The “Taste” of Fruit Tree Irrigation

It will not matter to some what instrumentation suggests about the characteristics of fruit harvested from trees grown under less than ideal irrigation. What matters to most is how the fruit tastes. A Spanish study was done to find out how peaches of the cultivar ‘Ryan’s Sun’ taste under different irrigation regimes fifty days prior to harvest. Peaches harvested from trees with no irrigation during those fifty days were delayed in their maturity and were smaller in size; trained tasters rated the fruits as being more firm, crisp, and sour. A panel of consumers indicated a reduced preference for fruit from such non-irrigated trees. Two of the irrigation regimes involved starting with full irrigation or none, and then switching. The trees that received irrigation closest to harvest had superior fruit quality according to the tasters. Peaches from trees receiving full irrigation, or irrigation nearest to harvest time, scored the highest marks.

            HortTechnology, December 2011 21 (6): 712-719

Keep Using That Mulch

Fraser fir (Abies fraseri) has no genetic resistance to several species of fungus (in the genus Phytophthora) that cause damaging and sometimes fatal root diseases when this conifers is grown as a Christmas tree. Management by the use of fungicides is not economically feasible. Cultural methods for managing Phytophthora root rot in field-grown Christmas trees was investigated at five different field sites in North Carolina. Cultural techniques evaluated included the use of mulches of wood chips, pine bark, or wood chips plus dairy compost, and the use of compost or sulfur as soil amendments. At several times during the two-year study, researchers took measurements of microbial populations, microbial activity, and organic decomposition activity in both soil and mulch layers. All of the variables measured were higher in the mulch layers than in the soil, at all times and at all sites. The type of mulch mattered little. At three of the sites, disease ratings and tree mortality were significantly lower where one or more of the mulches were used, compared to control fields without mulch at the same sites. The degree of organic decomposition activity had the greatest impact on reducing tree mortality.

            Plant Disease, May 2011 95 (5): 537-546

A Well-lit Place for Cuttings

According to studies done at Purdue University, in order to produce good quality rooted cuttings, more attention needs to be given to Daily Light Integrals, the total amount of photons that propagules receive each day. Many propagators focus on temperature, which is certainly an important factor in rooting speed. A certain minimum amount of light per day, in addition to the appropriate temperature, will help cuttings develop a robust root system, making for a higher quality plant in a shorter period of time.

            Hortscience, 47(1): 25-30