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- Author or Editor: J.H. Louw x
Absence or long delay of budbreak, also known as prolonged dormancy, is the most important symptom during incomplete dormancy. Budbreak number was evaluated to quantify seedling response to chilling and selection on excised and intact 1-year-old apple (Malus ×domestica Borkh.) seedlings under controlled and natural environmental conditions. Indices based on: 1) the number and distribution of budbreak (prolonged dormancy grade = PDG); 2) the number of buds breaking, including shoot length with increased budbreak as part of the calculation (prolonged dormancy index = PDI); and 3) budbreak number per 100-cm shoot (NB) were tested in association with budbreak time (TB). The indices expressed the effects of cold treatments that induce earlier and higher numbers of budbreak. PDI and NB, but not PDG, identified families with increased budbreak. Seedlings with high PDG and NB were also associated with families in which high chill requiring parents were used, indicating that TB as pre-selection criterion may fail to identify seedlings with increased budbreak. Response to pre-selection for increased budbreak using PDG could be verified with the PDS and NB indices in seedlings and seedling clones. The NB of intact 1-year-old shoots under natural conditions is recommended as a pre-selection criterion against prolonged dormancy in suboptimal winter conditions.
At its most basic, grafting is the replacement of one root system with another containing more desirable traits. Grafting of tomato (Solanum lycopersicum) onto disease-resistant rootstocks is an increasingly popular alternative for managing economically damaging soilborne diseases. Although certain rootstocks have demonstrated ancillary benefits in the form of improved tolerance to edaphic abiotic stress, the mechanisms behind the enhanced stress tolerance are not well understood. Specific traits within root system morphology (RSM), in both field crops and vegetables, can improve growth in conditions under abiotic stress. A greenhouse study was conducted to compare the RSM of 17 commercially available tomato rootstocks and one commercial field cultivar (Florida-47). Plants were grown in containers filled with a mixture of clay-based soil conditioner and pool filter sand (2:1 v/v) and harvested at 2, 3, or 4 weeks after emergence. At harvest, roots were cleaned, scanned, and analyzed with an image analysis system. Data collected included total root length (TRL), average root diameter, specific root length (SRL), and relative diameter class. The main effect of cultivar was significant (P ≤ 0.05) for all response variables and the main effect of harvest date was only significant (P ≤ 0.01) for TRL. ‘RST-106’ rootstock had the longest TRL, whereas ‘Beaufort’ had the shortest. ‘BHN-1088’ had the thickest average root diameter, which was 32% thicker than the thinnest, observed in ‘Beaufort’. SRL in ‘Beaufort’ was 60% larger than ‘BHN-1088’. This study demonstrated that gross differences exist in RSM of tomato rootstocks and that, when grown in a solid porous medium, these differences can be determined using an image analysis system.
Genetic variation in chilling requirement was investigated over three growth periods using clonal progenies of six apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] families derived from crosses of high and low chill requiring cultivars. Two quantitative measurements related to chilling requirement, viz., the time of initial budbreak (vegetative and reproductive) and the number of breaking buds over a specified time interval, were used as evaluation criteria. Genetic and environmental variances of the traits are presented as intra-class correlation coefficients for clones within and between families. For budbreak time, reproductive and vegetative, broad-sense heritability averaged around 75% and 69% respectively, indicating a high degree of genetic determination in this material. For budbreak number, moderate to low genetic determination was found with broad-sense heritabilities around 30%. Estimates of genetic components of variance between families were generally very low in comparison to the variance within families and predict potentially favorable responses to truncation selection on the traits within these progeny groups. Analysis of the data showed that distribution of budbreak time is typical of quantitative traits with means distributed closely around midparent values. Skewed distributions towards low budbreak number were obtained in varying degrees in all families.
Significant response to selection for budbreak number (NB) based on data recorded on 1-year-old shoots of young apple (Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.) seedlings (Expt. I) and branches from adult seedling trees (Expt. II) has been demonstrated in clonally propagated seedling trees. Between family variation for NB was low and masked by year × family interaction effects. Realized heritability for NB was estimated as 40% to 60%. Correlated response in uniformity and position of budbreak, and in the number and length of side shoots, was found. Association between the time of budbreak (TB) and NB, according to midparent and cross groupings, and according to the parental means, indicate a positive genetic correlation between these traits. Where data on adult trees were used as a measure of selection response and tested on young clonal trees, significant response and genetic variation was shown, confirming the presence of utilizable genetic variance and that this procedure may be successfully applied as an early screening method for increased budbreak in adult trees. Combined selection utilizing genetic variance between crosses as well as within crosses is proposed as the best procedure to increase the frequency of seedlings with increased budbreak and to improve adaptation to low winter chilling conditions.
Improvement of crop water use is imperative. Plants’ responses to limited water can dictate their ability to better use available resources and avoid prolonged and severe stress. The following study was conducted to determine how tomato (Solanum lycopersicum) rootstocks with different root system morphologies respond to drying soils. Plants were grown in pots containing an inorganic substrate composed of calcined clay and sand in a greenhouse on North Carolina State University’s campus. The heirloom tomato cultivar Cherokee Purple was used as the scion for ‘Beaufort’ and ‘Shield’ rootstocks as well as the self-grafted control. These rootstocks were assigned either normal or reduced irrigation treatments. Plants grown under the normal irrigation schedule were weighed and watered daily to maintain container capacity for one week. Those receiving reduced irrigation had all water withheld for one week, at which point strong midday wilting became evident. Shoot physiological and morphological data as well as root morphological data were collected at the end of the study. A constitutive positive increase on relative water content, leaf area, stomatal conductance (g
S), and net CO2 assimilation rate was observed with scions grafted on ‘Beaufort’. In addition, this rootstock had a significantly longer total root system (118.6 m) compared with ‘Shield’ (94.9 m) and the self-grafted control (104.2 m). Furthermore, 76.4% of the total root length observed in ‘Beaufort’ was composed of very thin diameter roots (
Interest and use of grafted tomato (Solanum lycopersicum) in the United States continues to grow. Pioneered in Asia, herbaceous grafting is a commonly used cultural practice to manage many soilborne pathogens. Bacterial wilt (BW), caused by the pathogen Ralstonia solanacearum, is an aggressive soilborne pathogen that affects tomato grown in the southeastern United States. Traditional fumigation methods have limited effectiveness in the management of this pathogen. The present study was conducted to compare the bacterial wilt resistance of three commercially available tomato rootstocks, which are purported to be resistant to bacterial wilt: ‘Cheong Gang’, ‘RST-04-106-T’, and ‘Shield’. The determinate hybrid tomato ‘Red Mountain’, which is susceptible to bacterial wilt, was used as the scion and nongrafted control. Three locations were used over 2 years in North Carolina: an on-farm site with a history of bacterial wilt and two North Carolina Department of Agriculture Research Stations with no recent history of bacterial wilt. No disease symptoms were observed in any of the three grafted treatments, whereas the nongrafted controls showed between 30% and 80% disease incidence at the on-farm location. The resultant rootstock-imparted resistance improved marketable yields by between 88% and 125% compared with the nongrafted plants. When grown in locations lacking BW there were no yield benefits to grafting with any of the three rootstocks.
The following study was conducted to address water use efficiency in grafted tomato (Solanum lycopersicum) in an on-farm environment. The commercial rootstock cultivars Beaufort (BE) and Shield (S) were chosen as these two have different root system morphologies that may benefit water use efficiency. The heirloom cultivar Cherokee Purple (CP) was grafted onto both rootstocks and used as the nongrafted control. The study was conducted in 2016 and 2017 on a 5-acre vegetable and cut flower farm in North Carolina’s Piedmont region. Plants were grown under protected, high-tunnel culture where they received either 100% (3 hours every other day) or 50% (1.5 hours every other day) of the grower’s normal irrigation regime. At 50% irrigation, ‘Beaufort’-grafted plants yielded significantly more than nongrafted ‘Cherokee Purple’ and ‘Shield’-grafted plants. Furthermore, ‘Beaufort’-grafted plants at 50% irrigation yielded more than nongrafted ‘Cherokee Purple’ receiving the 100% irrigation treatment. The ‘Beaufort’-grafted plants significantly improved irrigation water use efficiency (iWUE) at the 50% irrigation treatment compared with the other graft treatments. Yield and iWUE of ‘Shield’-grafted plants were comparable with the nongrafted ‘Cherokee Purple’ at both irrigation treatments. Regardless of irrigation treatment, grafting onto ‘Beaufort’ improved the quality of total fruit harvested. An economic assessment was conducted to determine the feasibility of using grafted plants in conditions lacking significant disease pressure. Purchasing grafted transplants would increase the initial investment by $5227.2 per acre. However, the increased yield obtained when using ‘Beaufort’ rootstock at 50% irrigation increased net revenue by $35,900.41 per acre compared with nongrafted ‘Cherokee Purple’ receiving 100% irrigation, amounting to a 44.6% increase in net revenue while saving ≈383,242 gal/acre of water per growing season. These results indicate that growers can select rootstocks to better manage water use in an environmentally friendly manner without limiting economic gains.
Tomato (Solanum lycopersicum L.) is a warm-season, cold-sensitive crop that shows slower growth and development at temperatures below 18 °C. Improving suboptimal temperature tolerance would allow earlier planting of field-grown tomato and a reduction in energy inputs for heating greenhouses. Grafting tomato onto high-altitude Solanum habrochaites (S. Knapp and D.M. Spooner) accessions has proven effective at improving scion suboptimal temperature tolerance in limited experiments. This study was conducted to determine whether commercially available tomato rootstocks with differing parental backgrounds and root system morphologies can improve the tolerance of scion plants to suboptimal temperature. Two controlled environment growth chambers were used and maintained at either optimal (25 °C day/20 °C night) or suboptimal (15 °C day/15 °C night) temperatures. The cold-sensitive tomato cultivar Moneymaker was used as the nongrafted and self-grafted control as well as scion grafted on ‘Multifort’ (S. lycopersicum × S. habrochaites), ‘Shield’ (S. lycopersicum), and S. habrochaites LA1777 rootstocks. Plants were grown for 10 days in 3.8 L plastic containers filled with a mixture of calcined clay and sand. ‘Multifort’ rootstock significantly reduced the amount of cold-induced stress as observed by larger leaf area and higher levels of CO2 assimilation and photosystem II quantum efficiency. ‘Multifort’ had significantly longer roots, having 42% to 56% more fine root (diameter less than 0.5 mm) length compared with the other nongrafted and grafted treatments. Leaf starch concentration was significantly lower in ‘Multifort’-grafted plants at suboptimal temperatures compared with the self-grafted and nongrafted controls and the ‘Shield’-grafted plants at the same temperature. The ability for ‘Multifort’ to maintain root growth at suboptimal temperatures may improve root system sink strength, thereby promoting movement of photosynthate from leaf to root even under cold conditions. This work demonstrates that a commercially available rootstock can be used to improve suboptimal temperature tolerance in cold-sensitive ‘Moneymaker’ scions.
Grafting of watermelon (Citrullus lanatus) is an established production practice that provides resistance to soilborne diseases or tolerance to abiotic stresses. Watermelon may be grafted on several cucurbit species (interspecific grafting); however, little research exists to describe root systems of these diverse rootstocks. A greenhouse study was conducted to compare root system morphology of nine commercially available cucurbit rootstocks, representing four species: pumpkin (Cucurbita maxima), squash (Cucurbita pepo), bottle gourd (Lagenaria siceraria), and an interspecific hybrid squash (C. maxima × C. moschata). Rootstocks were grafted with a triploid watermelon scion (‘Exclamation’), and root systems were compared with nongrafted (NG) and self-grafted (SG) ‘Exclamation’. Plants were harvested destructively at 1, 2, and 3 weeks after transplant (WAT), and data were collected on scion dry weight, total root length (TRL), average root diameter, root surface area, root:shoot dry-weight ratio, root diameter class proportions, and specific root length. For all response variables, the main effect of rootstock and rootstock species was significant (P < 0.05). The main effect of harvest was significant (P < 0.05) for all response variables, with the exception of TRL proportion in diameter class 2. ‘Ferro’ rootstock produced the largest TRL and root surface area, with observed values 122% and 120% greater than the smallest root system (‘Exclamation’ SG), respectively. Among rootstock species, pumpkin produced the largest TRL and root surface area, with observed values 100% and 82% greater than those of watermelon, respectively. These results demonstrate that substantial differences exist during the initial 3 WAT in root system morphology of rootstocks and rootstock species available for watermelon grafting and that morphologic differences of root systems can be characterized using image analysis.
The Center for Environmental Farming Systems (CEFS) is dedicated to farming systems that are environmentally, economically, and socially sustainable. Established in 1994 at the North Carolina Department of Agriculture and Consumer Services (NCDACS) Cherry Farm near Goldsboro, N.C.; CEFS operations extend over a land area of about 800 ha (2000 acres) [400 ha (1000 acres) cleared]. This unique center is a partnership among North Carolina State University (NCSU), North Carolina Agriculture and Technical State University (NCATSU), NCDACS, nongovernmental organizations (NGOs), other state and federal agencies, farmers and citizens. Long-term approaches that integrate the broad range of factors involved in agricultural systems are the focus of the Farming Systems Research Unit. The goal is to provide the empirical framework to address landscape-scale issues that impact long-run sustainability of North Carolina's agriculture. To this end, data collection and analyses include soil parameters (biological, chemical, physical), pests and predators (weeds, insects and disease), crop factors (growth, yield, and quality), economic factors, and energy issues. Five systems are being compared: a successional ecosystem, a plantation forestry-woodlot, an integrated crop-animal production system, an organic production system, and a cash-grain [best management practice (BMP)] cropping system. An interdisciplinary team of scientistsfrom the College of Agriculture and Life Sciences at NCSU and NCATSU, along with individuals from the NCDACS, NGO representatives, and farmers are collaborating in this endeavor. Experimental design and protocol are discussed, in addition to challenges and opportunities in designing and implementing long-term farming systems trials.