As with the N and K supply experiments, rootstock genotype was the major source of variation in shoot dry matter production under varying Si supply treatments, and volkameriana seedlings were more vigorous than seedlings of the other three rootstock genotypes (Table 10). Overall, plants grown with 2 mM Si in the nutrient solution produced approximately one third less shoot dry matter compared to seedlings grown without added Si.
As with the K and Si supply experiments, the major source of variation in shoot dry matter production under different pH treatments was rootstock (Table 14), and volkameriana seedlings were more vigorous than seedlings of the other three rootstock genotypes. The nutrient solution pH had no effect on dry matter production by any of the rootstock seedlings or on %N in shoot dry matter at harvest (Table 15).
Ed James has citrus in his veins. He has been working and thriving in the citrus business since he was a teenager — from hoeing orange trees to owning a caretaking business that serviced thousands of acres. That is, until about eight years ago.
In 2010, James looked around his personal 45-acre citrus grove and realized it was time to throw in the towel. The citrus industry in Florida had gone from over 800,000 acres to less than 400,000 acres. Citrus greening was the main culprit, but there were other factors for the decline. For James, it had just become completely unprofitable. The trees looked stunted and almost dead from foot rot, Diaprepes root weevil and HLB.
Choosing cover crops to enhance ecological services in orchards: A multiple criteria and systemic approach applied to tropical areas
Conventional agriculture is based on a high level of chemical inputs such as pesticides and fertilisers, leading to serious environmental impacts, health risks and loss of biodiversity. Pesticide reduction is a priority for intensive agricultural systems such as orchards. Reintroducing biodiversity in single crop systems can enhance biological regulations, and contribute to reduce the use of chemicals and to provide additional services such as run-off and erosion control. In tropical wet areas, weed control is difficult to manage without herbicides especially when orchards are not located in easily mechanised areas and when labour force is costly. Cover plants can be easily introduced in orchards and could be efficient in weed control and other functions. Based on this assumption, we developed a specific approach for the choice of adapted cover plants in single crop orchards to control weeds and provide additional ecological services. The approach was undertaken on citrus orchards in the French West Indies.
Institute for Micronutrient Technology, India
Potassium is an essential element for plant growth and is an extremely dynamic ion in plant and soil system. As an ion, potassium is highly mobile in the plant system but only moderately mobile in the soil system. Just like humans require a balanced diet with appropriate amounts of carbohydrates, proteins, vitamins, minerals, fats and water, plants too require conditions of balanced nutrition. There is a pre-determined ratio of nutrients that is required by the plant system, depending on its life cycle, environment and its genotypic characteristics, to realize its maximum genetic potential.
A recent visit to Japan for the annual Tokyo International Conference on African Development (TICAD), which was joined by the Citrus Growers’ Association at the behest of President Cyril Ramaphosa, provided the association with a salient opportunity to address some nagging aspects of fruit trade with that country, as well as to press the fruit industry’s interests.
Diane Nelson, UC Davis
In an orange grove outside Exeter, California, workers climb aluminum ladders to pick fruit with expert speed. California produces 80 percent of the nation’s fresh oranges, tangerines and lemons, most of it in small Central California communities like these.
“This may be the last place in the world where you can still grow citrus,” says farmer Richard Bennett, reaching high to pull an orange from a tree. He peels it in two long ribbons, and the scent of zest fills the air. “Citrus is so important to our health and economy, and it’s threatened by a devastating disease.”
Hiu-Ling Liao, Huiqin Chen & Kuang-Ren Chung
University of Florida, IFAS Citrus Research and Education Center
Postbloom fruit drop (PFD) of citrus is caused by the fungus Colletotrichum acutatum. The fungus infects flower petals causing brownish lesions that result in young fruit drop, leaf distortion, and formation of persistent calyces (commonly called ‘buttons’) after the fruitlet drops. Previous studies suggested that an imbalance of plant growth regulators such as auxin, ethylene, and jasmonic acid in C. acutatum-infected flowers, may contribute to young fruit drop.
Girdling increases carbohydrate availability and fruit-set in citrus cultivars irrespective of parthenocarpic ability
F. Rivas, M. Juan, V.Almela, M. Agusti
Departamento de Producción Vegetal, Cátedra de Citricultura, Universidad Politécnica de Valencia.
Departamento de Citricultura, Instituto Valenciano de Investigaciones Agrarias. Valencia, Spain
Department of Fruit Tree Sciences. Israel
The effects of girdling performed at various dates were evaluated during two consecutive years in high- and lowbearing commercial orchards of ‘Fortune’ mandarin and ‘Clausellina’ Satsuma mandarin. The time-dependent response was evaluated through fruitlet abscission, final fruit-set and yield as related to carbohydrate contents in developing fruitlets. A few days after treatment, girdling increased the soluble sugars content (SSC) in fruitlets, reduced the daily fruit drop, and thereby diminished abscission. Application of girdling to low-bearing ‘Fortune’ mandarin orchards was most effective 15 d before anthesis (DBA) and 35 d after anthesis (DAA). It increased yield by 125%. In high-bearing orchards, the best results were achieved by girdling 35 DAA, which increased yield by 28%.
Sarah Strauss, Davie Kadyampakeni, Ramdas Kanissery, Tara Wade, Lauren Diepenbrock and Juanita Popenoe
Cover crops are specific crops not intended for sale but for soil improvement and sustainability. They are increasingly common in the agricultural fields of the Midwest and other grain-producing regions because of the wide range of benefits not just for the soil, but also the cash crop. In those systems, cover crops improve water and nutrient retention, promote microbial activity, reduce weed growth and insect pests, and improve plant growth. Similar impacts have been found in tree crops like apples and peaches, where cover crops are planted in row middles.