Grafting can increase overall plant vigor and yield in the absence of disease or other stress, but studies in California focusing on grafting for increasing yield have found both increases and occasional decreases in yield when grafted to fresh market tomatoes . Therefore, absent developments that reduce the costs of these inputs, grafting is currently not economically feasible for processing tomato production in California. In addition to economic challenges with grafting, we encountered cultural issues with grafting in our experiments. Notably, we observed that the grafted and the tall grafted plants can outgrow the scion. The plants in the greenhouse and the field developed shoot growth from the rootstock, particularly in the tall grafted plants, likely due to the higher number of nodes on its rootstock stem compared to the standard grafted plants. This overgrowth was especially prevalent in 2019, in which a month after planting in the field, outgrowths of Maxifort were observed to emerge from the soil in between the grafted transplants. The different procedure used by the nursery to produce the transplants in 2019 compared to 2018 may explain the greater incidence of overgrowing the scion. Thus, black plastic pots for plants while the grafted plants reduce southern blight incidence, overgrown plants develop an undesirable taller vegetative canopy and produce unwanted fruit of the rootstock.
Although statistical and numeric trends suggest that increasing the height of the graft union may reduce southern blight incidence, the magnitude of this difference is small and not likely to make a practical difference in commercial production. The tall grafted plants did not develop as much southern blight as the non-grafted plants, but there are additional cultural issues with using the resistant rootstock in a processing tomato field such the risk of transplants breaking at their union while being transplanted or quickly after transplanting. Therefore, increasing the height of the graft union is likely not an economical approach for processing tomato production. We found a range of variation in susceptibility to southern blight among commercial cultivars. One Heinz cultivar was promising in 2018, although it developed disease in 2019. In 2019 one Harris Moran cultivar showed promise in its resistance to southern blight, but it was not evaluated in 2018 due to poor germination. We found the breeding lines reported by Leeper et al. 1992 to also perform well in one replicate year in greenhouse conditions, therefore these breeding lines may be beneficial for southern blight resistance breeding for California processing tomatoes. However, three of the breeding lines performed similarly to two Heinz and one Nunhmens cultivars that are already planted in the southern San Joaquin Valley. The cultivars that performed well in our experiments may have lower susceptibility to southern blight compared to other cultivars and thus may be options for growers to plant in fields with a history of southern blight.While results from the cultivar experiments were promising, cultivars could not be separated easily when evaluating their risk of developing disease.
The disease risk ranking of some cultivars changed drastically between the two experimental replications: a few cultivars with low risk in 2018 developed more disease in 2019 and vice versa, but several cultivars were in the highest risk tier in both years. Although cultivars were difficult to separate, the study in 2019 developed more disease than the study in 2018. This may have been due to excessively high irrigation pressure in two blocks of the 2018 study that is suspected to have washed the inoculum out of pots, resulting in minimal disease development. Further evaluation of these cultivars in the greenhouse and the field is needed to confirm these findings. Disease incidence was low overall in the greenhouse grafting studies, especially in HZ 8504 compared to HZ 5608. This may be due to our experimental setup in which plants were trellised because of space constraints on the greenhouse bench. When plants were trellised, the stem did not branch near the soil line, and vegetative tissues did not touch inoculated soil, while in the field the vegetative canopy is at risk of coming into contact with sclerotia in the soil. The utility of greenhouse experiments for evaluating the effect of grafting on southern blight may be limited. These studies showed promising results for the management of southern blight in California. Based on our studies, the approach of grafting for management of southern blight may not be the best application. The use of resistant cultivars is a better and accessible approach for California processing tomato growers.
We recommend the development of field studies to evaluate the promising cultivars in the greenhouse under natural conditions.Raspberry fruit are produced on a perennial shrub belonging to the vastly diversified Rubus genera of the Rosaceae family. There are mainly two types of raspberries: red and black. Yellow raspberries are a mutated version of red raspberries that prevents the formation of red color . Purple raspberries are a hybrid between black and red raspberries. Raspberries are an aggregate fruit, a combination of individual drupelets that stay together with the help of an invisible hair-like structure. Each small drupelet is developed from a carpel, a significant characteristic of Rubus, where the mesocarps become fleshy and the endocarps become hard and form a tiny pit that encloses a single seed within each drupelet. . The drupelets separate from the receptacle at harvest, creating a hollow, thimble-shaped fruit.The primary planting material for raspberries is the cane. Cane traditionally refers to aerial raspberry shoots but also often refers to rooted suckers . Raspberry plants generally start fruiting in the second year and can continue up to 15 years if properly managed. However, the canes are biennial. Usually, the cane grows in one year and fruits the next year. Canes sprouting in the first year are called primocanes , and in the second year are called floricanes . Both canes are present during the growing season . Primocane-fruiting types can produce two crops per year; onein the summer from the floricanes and the other in the fall from the primocanes. With the onset of cold temperatures, floricanes often go into a period of dormancy. Six weeks or more at 4℃ or lower is required to break dormancy. After fruiting, the entire cane senesces and dies. When second-year canes are flowering, first-year canes are growing from the crown or roots. Like other brambles, raspberry is a self-pollinated species . Fruit development occurs for 30-36 days in most cultivars . The best yields take place under sunny, cool summer conditions . Recently, the use of the high tunnels has extended the berry cultivation season both at the beginning and the end. This extension enables growers to gain more profit from the market as berry prices are usually higher during early and late seasons . Like all crops, water is very important for raspberry production. According to Prange and DeEll , lack of water can affect the production and quality of berry fruit after harvest. However, excessive water, mostly due to high rainfall during the fruit growing period, drainage pot made raspberries more susceptible to mechanical damage during transportation and storage .The red raspberry is believed to have originated in Turkey’s Ide mountains. The Romans may have expanded raspberry cultivation throughout Europe. However, the British improved and popularized raspberries throughout the middle ages and had the plant exported to New York by 1771 . In the early 1900s, raspberry cultivation got its momentum, and in 1920, New York State growers harvested more than 10,000 acres of raspberries. In 2018, there were three major raspberry production regions: Russia, Europe , and the Pacific Coast of North America . World raspberry production has grown 80% over the last 10 years. From 2010 to 2019, production increased from 373,000 tons to 684,000 tons. . In 2020, the total area under raspberry cultivation in the United States was 16,900 acres producing 111,000 tons of raspberries valued at US$469 million. In California, there were 8,000 acres, valued at US$395 million for fresh raspberries only. Canada is the biggest importer of US raspberries, and in 2021, Canada imported a total of 24,400 tons of fresh raspberries valued at $154 million from the US .
A fruit’s quality is generally assessed based on its visual appearance, texture, flavor, and nutritional compounds . Raspberry quality and shelf life can be adversely affected by a variety of pre-harvest and post harvest factors. Pre-harvest factors include genetics, environment, and cultural practices. Postharvest factors such as handling, transportation, storage temperature, condition and duration, relative humidity also play important role on maintaining raspberry fruit quality. Raspberry is renowned for its aroma and flavor. Raspberry is a non-climacteric fruit and their taste and flavor mostly develop while they are ripening on the plant. The ratio of sugar and organic acids determines raspberry taste . Soluble solids from 9 to 10% and titratable acidity from 1.5 to 1.8% constitute good raspberry taste according to De Ancos . Wang et al. evaluated raspberry fruit harvested at 5%, 20%, 50%, 80% and 100% ripe and they concluded that berries that were 50% to 80% ripe developed the same degree of SS, TA, and sugars as berries that were 100% ripe, whereas berries that were 5 to 20% ripe neverattained those properties. There are many volatile compounds, notably, α and β-ionone, linalool, α and β-pinene, caryophyllene and citral, contributing to raspberry flavor . Berry purchases are linked to several factors, the most important being freshness and origin, while price does not play a significant role . Visual quality is also very important for raspberry and a good indicator of shelf life. Brighter color without any visible decay and leakiness is perceived as fresher. Krüger et al. categorized raspberries in three groups based on their ripening stage; semi-ripe, ripe and over-ripe. They concluded that semiripe raspberries were potentially more suitable for shipping while maintaining acceptable sensory quality .Consumers have always been concerned about food quality and appearance, in general. However, consumer preference has been shifting toward fruit flavor and nutritional qualities, including their composition and level of bioactive compounds, such as vitamins, minerals, fiber, and even phenolic compounds . Raspberry fruit are 85- 90% water, ~9% SS and the remaining are insoluble solids. Raspberry fruit contain 13.6–31.1 mg/100 g Vitamin C and 0.2–83.6 mg/100 g anthocyanins . These compounds vary by cultivar, harvest time, cultural practices, environment and weather conditions . Raspberry fruit also contain a broad range of polyphenolic compounds; phenolic acids, flavanols, anthocyanins, proanthocyanidins, and ellagitannins . These compounds have been extensively studied for their antioxidant capacity and impact on human health . High antioxidant capacity is believed to contribute to health benefits by ameliorating the detrimental effects of reactive oxygen species generated in the body through oxygen metabolism . Berry polyphenols also have been shown to protect against ROS-induced neurological diseases such as Alzheimer’s , and red raspberries have been reported to have a neuroprotective effect . However, the impact of raspberry fruit’s high antioxidant capacity might be limited by very low uptake into the bloodstream from dietary intake . Nonetheless, they could have beneficial effects on the gastrointestinal tract as they pass along the digestive system, thus preventing oxidation from foods already in the stomach and GIT or by affecting food digestion, glucose levels, and calorie usage . In addition, raspberry contains a significant amount of ellagitannins; a large group of polyphenols that are beneficial to fight cervical cancer, cardiovascular disease, and diabetics .Raspberries have a short shelf life of 2 to 5 days because of their natural soft texture and sensitivity to mold and other pathogens. Postharvest handling and storage conditions, including packaging, relative humidity, temperature, and light, can affect the bioactive compounds in brambles . Low temperatures slow pathogen growth and reduce the rate of deterioration of freshly harvested commodities, thus extending shelf life and the marketing period . The recommended temperature for raspberry storage is 0-1℃ , but it is challenging to maintain this recommended temperature during transportation and marketing. Although low storage temperatures can slow the development of Botrytis cinerea infections, they do not provide adequate control when pathogen inoculum loadsare high . Acidity and SS as well as pigment compounds such as anthocyanins play an important role in berry marketability after storage , and the presence of light and temperature during storage might affect anthocyanin compound stability .Modification of storage or transport atmospheres help maintain raspberry shelf life and quality.