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Rabbiteye blueberry (Vaccinium virgatum) bushes are relatively easy to grow and commonplace across Mississippi; however, if not properly maintained, the bushes will decline over time. Eighteen, aged, low-productivity ‘Woodard’ rabbiteye blueberry bushes were pruned at two different heights (ground level and a 50-cm above ground level) after harvest in July 2017, and phosphorous acid was applied as a drench and foliar spray in the first year, but this was discontinued as the applications had no effect on the bushes. For two seasons, fruit yields were collected and weighed, bushes were measured for growth parameters, and canes were weighed. Bushes pruned at the 50-cm above ground level had much higher yields in both 2019 (3.47 vs. 0.63 kg) and 2020 (3.91 vs. 1.23 kg), thus providing a substantial yield benefit. The 50-cm above ground level pruning treatment bushes produced more canes by the end of the study, therefore accounting for more fruiting area, as seen in the harvest index. In short, pruning old, nonproductive bushes at a 50-cm above ground level can provide growers with greater potential for early economic returns than pruning at ground level, for ‘Woodard’ rabbiteye blueberry.
Petunia × hybrida Vilm. cvs. `Purple Wave', `Celebrity Burgundy', `Fantasy Pink Morn', and `Dreams Red' were treated with temperature and photoperiod treatments for different lengths of time at different stages of development during the first 6 weeks after germination. Plants were grown with ambient light (≈8–9 hr) at 16°C before and after treatments. Flowering was earliest and leaf number below the first flower was lowest when plants were grown under daylight plus 100 μmol·m–2·s–1 continuous light (high-pressure sodium lamps). Flowering did not occur when plants were grown under short-day treatment (8-hr daylight). Plants grown with night interruption lighting from 2200–0200 HR (2 μmol·m–2·s–1 from incandescent lamps) flowered earlier, and with a reduced leaf number compared to plants grown with daylight + a 3-hr day extension from 1700–2000 HR (100 μmol·m–2·s–1 using high-pressure sodium lamps). Plant height and internode elongation were greatest and least in night interruption and continuous light treatments, respectively. `Fantasy Pink Morn' and `Purple Wave' were the earliest and latest cultivars to flower, respectively. Flowering was hastened as temperature increased from 12 to 20°C, but not as temperature was further increased from 20 to 24°C. Branching increased as temperature decreased from 24 to 12°C. Implications of data with respect to classification of petunia flower induction and pre-fi nishing seedlings are discussed.
Viola × wittrockiana Gams. cvs `Delta Pure Rose' and `Sorbet Yellow Frost' were grown under different photoperiod and temperature treatments (12–24 ± 2°C) for different lengths of time at different stages of development during the first 6 weeks after germination. Plants were grown with ambient light (≈9 hr) at 16°C before and after treatments. Days to anthesis and leaf number were lowest when plants were grown under night interruption from 2200–0200 hr (2 μmol·m–2·s–1 from incandescent lamps) and daylight plus continuous light (100 μmol·m–2·s–1 from high-pressure sodium lamps) for `Sorbet Yellow Frost' and `Delta Pure Rose', respectively. Days to anthesis decreased as temperature increased from 12 to 24°C. Plant height and internode elongation were greatest and least in the night interruption and continuous light treatments, respectively. Branching decreased as temperature increased from 12 to 24°C. Implications of these data with respect to classification of Viola × wittrockiana flower induction and development of prefinished seedlings is discussed.
White drupelet disorder (WDD) in blackberry (Rubus subgenus Rubus) is an abiotic condition resulting from a cultivar and environment interaction. Although high temperatures and light intensities have been implicated, little is known why this disorder manifests. Other factors, such as overall plant stress, may be contributing influences. In this study, three treatments were applied to examine whether the addition of nitrogen (N) can reduce WDD on ‘Sweetie Pie’ erect blackberry over three seasons. An initial 50 lb/acre (56.0 kg⋅ha–1) N was applied to all plots at budbreak. Two additional N application treatments of 100 kg⋅ha–1 were applied at one time (1×) or five, 20-kg⋅ha–1 applications (5×), spaced 1 week apart for 5 weeks starting at bloom. One control treatment of no additional N (0×) was also included. Berries were harvested and weighed as a total, then berries with white drupelets were separated out and weighed. The two values were divided to create a proportion and were then multiplied by 100 to determine the percentage. Nitrogen application decreased the percentage of white drupelet berries from 13.0% (control) to 10.0% (one additional application) and 9.1% (five additional applications). WDD for the 0× treatment correlated negatively to maximum high daytime temperatures during May (r = –0.58, P = 0.03) over the three seasons. Occurrence of white drupelets by treatments 0×, 1×, and 5× correlated significantly with the cumulative number of rainfall events (r = 0.49, 0.47, and 0.46, respectively). Leaf chlorophyll index and photosynthesis measurements were unaffected by treatment. Although it is likely that multiple factors are involved in the development of white drupelets, additional N may reduce the problem.
White drupelet disorder (WDD) is a problem that occurs during the ripening stage in some blackberry (Rubus subgenus Rubus) cultivars. Although berries affected with a few white drupelets may taste fine, they are unpleasant aesthetically, and this may lead to negative consumer perceptions and economic ramifications. During 2 years of observational studies and field trials (2016 and 2017), we evaluated changes in three susceptible cultivars in Mississippi affected by WDD. ‘Chickasaw’, ‘Kiowa’, and ‘Sweetie Pie’ berries were harvested twice per week and assessed for WDD. Weather conditions differed substantially during harvest in 2016 and 2017, with 2017 being cooler and rainier which resulted in a lower incidence of WDD. Compared with 2016, in 2017, the overall percentage of berries exhibiting WDD dropped from 22% to 12% for ‘Sweetie Pie’, 6% to 3% for ‘Chickasaw’, and 8% to 3% for ‘Kiowa’. The soluble solids concentration was highest in ‘Sweetie Pie’, 11.9% and 9.5% for 2016 and 2017, respectively. For all cultivars examined, the soluble solids concentration of extracted white drupelets was substantially lower than regular drupelets. The value for skin break force for white drupelets was higher than that for black drupelets, 0.99 N vs. 0.29 N, respectively. In 2017, an about 30% shadecloth treatment had a significantly positive impact by decreasing WDD symptoms in all cultivars by 63% when compared with non-shaded plants, but soluble solids concentration was lower. Our results indicate that rain and shadecloth decrease symptoms of WDD. Therefore, growers may be able to use overhead irrigation and shade to reduce WDD symptoms.
The effect of supplemental lighting on strawberry growth and anthracnose disease response of three strawberry (Fragaria ×ananassa) cultivars was evaluated in two greenhouse trials, and the effect on strawberry anthracnose pathogens (Colletotrichum sp.) was evaluated in the laboratory. The objective of the greenhouse trials was to determine the effect of various intensities of the red and blue light emitting diode (LED) light treatment on strawberry plant vigor, injury, and disease development. In these trials, the duration of supplemental light treatments was split into two 4-hour periods: dawn and dusk. The intensity of the red and blue LED bulbs was set using an adjustable dial at 1 or 3 in trial 1 and at 1, 5, or 10 in trial 2. Illuminance and photosynthetic photon flux densities of the light treatments ranged from lows of 402 lx and 5 μmol⋅m–2⋅s–1 (blue LED 1) to highs of 575 lx and 25 μmol⋅m–2⋅s–1 (red LED 1 + blue LED 3) in trial 1, and from lows of 4213 lx and 81 μmol⋅m–2⋅s–1 (red LED 1) to highs of 7051 lx (red LED 5) and 194 μmol⋅m–2⋅s–1 (red LED 10) in trial 2. Lower light intensities in trial 1 resulted in no significant differences as a result of light treatments in relative chlorophyll content, plant vigor ratings, or disease severity ratings (DSRs). However, plant injury ratings were significantly greater in plants in the wide-spectrum fluorescent (WSF) plus ultraviolet B (UVB) light treatment compared with the other treatments. Under the higher light intensities in trial 2, there were more significant effects among light treatments. Relative chlorophyll content of plants in the WSF + UVB, WSF, and red LED 1 treatments was significantly greater than that of plants in the red LED 10 treatment; however, plants in the red LED 10 treatment had the greatest injury ratings. Detached leaves from plants in the red 5 LED and red 10 LED treatments inoculated with Colletotrichum gloeosporioides received the greatest DSRs, and leaves from plants in the red LED 1 and WSF treatments received the lowest DSRs. In the laboratory, five days of exposure to supplemental lights did not prevent the growth of isolates of three species of Colletotrichum pathogens even though the intensity of the LED lights was set at their highest intensity. However, growth of isolates exposed to the WSF + UVB light treatment was slowed.
Mentha longifolia, a wild relative of the polyploid, cultivated Mentha (mint) species, was evaluated as a potential model system for genetic research relevant to the cultivated mints. Fourteen Mentha longifolia accessions maintained by the US Department of Agriculture (USDA), Agricultural Research Service, National Clonal Germplasm Repository (NCGR), were highly diverse with respect to geographic origin, oil composition, verticillium wilt resistance, aspects of morphology, and molecular marker polymorphism. Accession CMEN 584 was the only carvone chemotype, while CMEN 682 was the only accession with high menthol content. Trans-piperitone oxide was the primary oil component of accessions CMEN 17 and CMEN 18, while pulegone was most abundant in CMEN 20, CMEN 500, CMEN 501, and CMEN 585. Four accessions—CMEN 585, CMEN 17, CMEN 501, and CMEN 81—were consistently resistant to verticillium wilt, while CMEN 584 and CMEN 516 were highly susceptible. Pairwise similarity coefficients were calculated and a UPGMA (unweighted pair-group analysis) tree was constructed on the basis of 63 informative randomly amplified polymorphic DNA (RAPD) marker bands. CMEN 585 and CMEN 584 shared the greatest number of bands (16), and formed a distinct cluster in the UPGMA tree. Seven pairs of accessions had no bands in common, emphasizing the high degree of molecular diversity represented by these accessions. The favorable features of diploid (2n = 2x = 24) genome constitution, comparatively small genome size (400 to 500 Mb), self-fertility, fecundity, and diversity with respect to economically relevant traits, contribute to M. longifolia's potential usefulness as a model system for the cultivated mints. As a perennial species amenable to vegetative propagation, M. longifolia's spectrum of susceptibility/resistance to an important vascular wilt disease encourages its further evaluation as a system for broader studies of plant–microbe interactions and disease resistance mechanisms.