The three varieties of Caribbean pine have significantly different amounts of nuclear DNA: Pinus caribaea var. caribaea, 11.5; P. caribaea var. hondurensis, 21; and, P. caribaea var. bahamensis, 25 pg. Dormant embryos of the three varieties had more nuclear DNA than germinating seedlings, and this extra DNA was spread through several classes from 2C to 7C; however, upon germination the seedling DNA rapidly reorganizes into the 2C–4C distribution typical of diploid plants. DNA content polymorphism of the dormant embryos among the three varieties was directly correlated with the diploid amount of DNA and with needle and cotyledon diversity. Buds regenerated from dormant embryo explants in tissue culture were genetically stable; however, the roots of regenerated plants had DNA contents ranging up to nine times the haploid amount. The instability is ascribed to the auxin content of the rooting medium, but buds regenerated or growing on this medium were stable. This bud stability and the production of buds on needle explants from 13-month-old regenerated seedlings are positive indicators for Caribbean pine biotechnology.

High temperatures and drought are common stresses limiting crop growth and productivity in subtropical regions where citrus are produced. In addition to impacts on physiological processes such as transpiration, photosynthesis, and respiration, excessive solar radiation can also reduce fruit productivity by inducing physiological disorders such as sunburn. This study evaluated the effects of radiation reflectants and anti-transpirants on leaf physiology, and fruit sunburn in grapefruit trees (Citrus x paradisi Macfs. cv. Rio Red) in south Texas during the 2016 and 2017 growing seasons. Two calcium-based reflectants, and a methene/pinolene-based anti-transpirant were foliar applied to fruit-bearing trees. Reflectants reduced fruit and leaf temperatures by 0.2°C and 0.21°C, respectively, while the anti-transpirant treatments increased fruit and leaf temperature by approximately 0.83°C and 0.2°C relative to the controls. Stomatal conductance decreased by 1.3% and 3.3%, respectively, in response to the reflectant treatments, while anti-transpirant treatments resulted in decreased stomatal conductance (8.3%) relative to the controls. More sunburned fruit were found in anti-transpirant treated trees in both years (6% and 8.2% for 2016 and 2017) and the reflectant treatments reduced sunburn incidence by 4.9% and 1.8% in those years. These observations indicate that reflectant applications could be a viable strategy to mitigate heat/radiation stress and sunburn in grapefruit.

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Red and black spruce and their hybrids can be determined by morphological indices; however, the criteria are somewhat subjective and increasingly difficult to use at higher elevations. Although the chromosome number is identical (2n = 24), red spruce has twice as much nuclear DNA (48 pg) than black spruce (24 pg) and thus the species and their hybrids can also be separated by cytophotometry. This is relevant to spruce decline studies because black spruce is much more resistant to high elevation environmental stresses, both natural and anthropogenic. It also has implications for the effect of climatic changes on the composition of high elevation spruce-fir forests because red spruce can outcompete black spruce under more mesic conditions. Four elevation transects sampling spruce on the east and west sides of Mount Washington (New Hampshire) and Camels Hump (Vermont) and a single transect on the southwest side of Whiteface Mountain (New York) were made to investigate the degree of hybridization and introgression between these two species. A positive correlation was found between increased elevation and increased black spruce genes on Mount Washington and Camels Hump. Pure black spruce was found on Mount Washington from 1356 m to 1582 m. No pure black or red spruce was found on Camels Hump although the proportion of red spruce alleles was significantly greater on Camels Hump. All trees sampled at all elevations on Whiteface Mountain were pure red spruce. Thus the proportion of black spruce alleles in high elevation spruce populations decreases from east to west. This closely parallels the increase in spruce decline which increases from east to west.