Emily Hoover

Biological Mulches for Managing Weeds in Transplanted Strawberry (Fragaria × ananassa)1

Diminishing availability and increasing costs of herbicides cause strawberry growers to seek both chemical and nonchemical alternatives, especially for within-row weed control soon after strawberries are transplanted. Several weed control treatments for strawberry establishment were examined during 2 yr in Minnesota. Treatments included: woolen landscaping fabric centered over the crop row; as above, but 2-ply fabric; spring canola incorporated into soil when 30 cm tall; as above, but canola killed with burndown herbicide and left as mulch; standard herbicide, DCPA; hand weeded; and no weed control. Areas between all strawberry rows were cultivated. Measurements included weed densities and weights, numbers of strawberry daughter plants, and fruit yield 1 yr after transplantation. The best alternative treatment was the 1-ply woolen fabric. It nearly eliminated weeds from rows, promoted daughter plant rooting, and allowed maximum fruit yields, equivalent to those of the DCPA and hand-weeded treatments. Canola mulch controlled weeds inconsistently and achieved only modest to low production of daughter plants and fruit. Weed control and fruit yield with incorporated canola were similar to the weedy check treatment. Nomenclature: DCPA; canola, Brassica napus L.; strawberry, Fragaria × ananassa Duchesne ‘Glooscap’. Additional index words: Cover crop, landscape fabric, weed control, weed management.

Seasonal variation in the onset and duration of flower development in 'Royal Gala' apple buds

Summary The formation of bud scales, transition leaves, true leaves, bracts and flower primordia were observed in buds removed from non-flowering sites on one year old shoots of apple ‘Royal Gala’. Buds were sampled from trees in Hawkes Bay, New Zealand (latitude 398S) during six successive seasons. The onset of flower development varied between seasons from 72 to 99.d after full bloom. Floral development was poorly synchronized within the populations of sampled buds, lasting 22 to 50.d. Differences in the onset and duration of flower development could not be related to seasonal differences in heat accumulation from full bloom. There was significant variation between seasons in the minimum number of appendages observed within buds that exhibited doming, which indicates floral development. In the 1998/99 season, doming was observed in buds that had only 15.7 appendages, whereas in the 1999/2000 season the minimum number of appendages within a bud that had initiated flowers was 17.5. When the data from all seasons were considered, the rate of appendage formation within developing buds was not consistently related to heat accumulation.

The Effect of Calcium Sprays and Fruit Thinning on Bitter Pit Incidence and Calcium Content in ‘Honeycrisp’ Apple

ABSTRACT ‘Honeycrisp’ is a recently released cultivar of apple (Malus x domestica) developed by the University of Minnesota, now in high demand by growers and consumers. This cultivar is susceptible to bitter pit, especially when the trees are young and the fruit load is low. The effects of calcium (Ca) sprays, fruit thinning, vegetative growth, fruit and leaf nutrient concentration on bitter pit incidence, and two sampling methods for nutrient analysis were studied. Bitter pit incidence was associated with several variables, including Ca and phosphorus (P) concentrations in leaves and fruits, magnesium (Mg) concentration in leaves, and yield parameters. Fruit Ca concentration and content for the growing season were modeled, which allowed the determinations of Ca levels associated with bitter pit incidence. Our data suggest that plug analysis was less sensitive than fruit-segment analysis for finding differences in Ca concentrations.

Solanum torvum as a Compatible Rootstock in Interspecific TomatoGrafting

Two tomato scions (‘Celebrity’ and ‘CLN3212A’) were grafted onto Solanum torvum and tomato ‘Maxifort’ rootstock to determine compatibility. Experimental design included self-grafted and non-grafted control rootstocks. Seed vs. vegetative S. torvum rootstocks were also compared to further explore grafting options. Average number of days for graft fusion and survival rate was measured for each scion/rootstock combination. Vegetative S. torvum cuttings had the poorest grafting success rate as a rootstock (50% for both scions), while all other rootstock genotypes had statistically similar or higher success rates. There was no significant difference in time to graft fusion among any grafted genotypes. High compatibility of seed-derived S. torvum suggests its potential use as an interspecific grafting rootstock in areas where access to seed is readily available.

Bud development and floral morphogenesis in four apple cultivars

Summary Buds were sampled from non-flowering spurs that had developed on 1 year-old wood of four apple (Malus domestica Borkh.) cultivars during the 1998-99 growing season in order to determine the effect of cultivar on appendage formation, doming and flower morphogenesis. Cultivars differed in their pattern of appendage formation over time. The rate of appendage formation was highest in ‘Fuji’ and ‘Pacific Rose™’ and lowest in ‘Braeburn’ during the first 60 d after bloom (DAB). A high proportion of buds were floral in all cultivars at the end of the growing season (75–100% depending on cultivar). However, the probability of observing doming was never greater than 0.13, indicating that flower morphogenesis proceeded rapidly once buds were committed to floral development. The four cultivars each exhibited a unique pattern of floral development, as determined by fitting response probabilities to each of five ordinal stages of development with time. Doming occurred significantly earlier in ‘Fuji’ buds (peaking 86 DAB) than in buds of the other cultivars (peaking 104–112 DAB). Doming was initiated at the same time in buds of ‘Braeburn’, ‘Royal Gala’ and ‘Pacific Rose™, but was completed earlier in ‘Braeburn’ than in ‘Royal Gala’. The timing of floral commitment was not related either to the time of flowering, or to the time of fruit maturity of the cultivar. These observations indicate that the timing of specific events during flower morphogenesis differed between cultivars.

Yield and quality characteristics of day-neutral strawberry in the United States Upper Midwest using organic practices

Abstract The Upper Midwest of the US accounts for an extremely small portion of national strawberry (Fragaria x ananassa) production due to the prevalence of ‘June-bearing’ cultivars, which are limited to a short six-week fruiting window from June to early July. Determination of high yielding and high quality organically managed cultural practices for newer day-neutral cultivars in the region was performed. Six day-neutral cultivars were planted at two locations (St. Paul, and Morris, MN) in 2013 and 2014 and organically managed as annual crops under straw mulch, plastic mulch, and plastic mulch with low tunnel cultural practices. Yield and average berry weight for each cultivar/cultural practice combination was collected and analyzed weekly and cumulatively at each location and year. Total phenolic content (TPC) and total soluble solid (TSS) content of fruit was measured as indicators of nutritional and sensory quality over time. Day-neutral production added an average of fourteen weeks to the June-bearing strawberry season regardless of cultural practice, while all practices yielded more fruit than the 6160 kg ha–1 average for June-bearing production in the region. Significant cultivar differences within each practice were observed as well. TPC and TSS both displayed significant cultivar and time of harvest effects. Overall our data support the conclusion that day-neutral strawberries can perform well using organic cultural practices in the Upper Midwest, providing growers the opportunity to extend the season and bolster yield, while providing consumers access to nutritious, locally available fruit for a longer period of time.

DNA content of Phaseolus coccineus x P. vulgaris suspensors

SummaryAt the globular stage of embryo development, the level of DNA, as determined from microspectrophotometric analysis of Feulgen-stained squashes, was significantly higher in the interspecific hybrid suspensor than in suspensors from self-pollination of Phaseolus coccineus, the maternal parent. However, at the early-heart and early-cotyledonary stages of development, DNA content of interspecific hybrid suspensors was significantly lower than that of suspensors formed after self-pollination of either P. coccineus or P. vulgaris. The relationship between DNA content and suspensor cell length for P. coccineus and P. vulgaris at all developmental stages and between DNA content and cell area for P. coccineus at the early-cotyledonary stage was altered in hybrid suspensor cells. Nuclei in large cells of interspecific suspensors exhibited uneven distribution of polytene chromosomes and no clear nuclear outline.

Partitioning of 14C-photoassimllates within seeds of Phaseolus coccineus (Lam.) and Phaseolus coccineus x Phaseolus vulgaris L.

The objective of this study was to determine partitioning within seeds of 14C-photoassimilates at three stages of seed development in two Phaseolus crosses — P. coccineus Lam. selfed, and P. coccineus x P. vulgaris L. Abortion of the interspecific embryos occurred when the seed reached 10 mm seed length. When expressed as sink strength (% dpm) or sink activity (% dmp/d.wt.) there were no differences in partitioning of 14C-photoassimilates when whole seeds were analyzed. If the seed was divided into seed coat, liquid endosperm, and embryo, the sink activity of the interspecific embryo was higher than that of the embryo in the selfed seed. Therefore, abortion of these interspecific Phaselus embryos appeared not to be caused by a lack of photoassimilates.