Written by Bernardita Sallato, WSU, Nov 19, 2018
A team of Washington State University researchers, led by Bernardita Sallato, tree fruit extension specialist, have recently initiated a 3-year project funded by WSDA. The project will focus on root growth management to reduce calcium (Ca) deficiency disorders in apples and cherries.
Calcium deficiencies are at the root of many tree fruit disorders worldwide. In most cases, these disorders are named to reflect their symptoms – bitter pit in apples, cork spot in pears, creasing in oranges, brown rot in tomato, etc (Shear and Faust, 1980). A deficiency in calcium is also implicated in greater susceptibility to other fruit quality problems such as lenticel breakdown, cracking, and sunburn (Shear and Faust, 1980). Unfortunately, unlike other nutrient deficiencies, Ca disorders cannot be solved by simply applying more Ca (de Freitas et al., 2010)
Calcium is one of the most complex nutrients in the plant due to its many roles. It is essential for cell structure, environmental responses, and as a cofactor for numerous processes. Calcium’s form and intra-cellular location (e.g., cytosolic Ca2+, vacuolar Ca-oxalate, cell wall Ca-pectate), and concentration, are highly regulated for each distinct function. The complexity of calcium’s role in the plant is one of the reasons that Ca sprays often yield inconsistent or contradictory results (Atkinson, 1979)
In the last 50 years, there has been great progress toward understanding calcium’s role in fruit crops and how to mitigate calcium-related disorders. In this new project, our approach is to focus on early season root growth management to reduce calcium-related disorders. This concept is built from previous key findings associated to Ca biochemistry, absorption, and distribution. We know that Ca absorption occurs mainly through new root tips (Marschner, 2002), and that these new root tips are initiated during active root growth. Root growth patterns can vary, but in most cases occurs during spring when conditions are adequate for root growth. The key environmental factors controlling root growth are temperature and nutrient availability. Adequate temperatures for root growth in apple appear to be above 54 ºF (Hogue and Nielsen, 1987). In WA production regions, soil temperatures are often cool in the spring, particularly with heavy soils, cold winters, or when growers irrigate early for frost protection. Calcium for cell wall development is required during the first growing stages when absorbed Ca is partitioned to building fruit cell walls (Marschner, 2002). In most species this occurs between flowering and the end of cell division (about two weeks before pit hardening in cherries and approx. 40 DAFB in apples). During this period, absorbed Ca is partitioned to the fruit, before vegetative growth is significant, and out-competes fruit for Ca. Therefore, our project will focus on evaluating the effect of early root growth on Ca absorption and distribution towards the fruit, and its impact on fruit quality.
The management practices for manipulating uptake of Ca will vary among orchards – we will consider increasing soil temperature during spring, root pruning for root tip development during cell division, reduce abiotic limiting factors, and manage nutrient availability in the soil. In addition, we will evaluate different methods for determining Ca content in fruit. Total Ca (typically determined) does not correlate well with Ca deficiency disorders, as it does not distinguish between cell wall, membrane, soluble or insoluble forms of Ca in the tissue. Our evaluations will account for these distinct locations and forms of Ca in the fruit using a method developed previously (Ohat et al. 1970, cited by Dong et al. 2004).
Our first year we will be looking for tree fruit sites with historic Ca deficiency disorders conditions. We will also evaluate sweet cherry orchards with fruit quality problems for an initial prospection. Growers located in South Central WA; Yakima Valley to North Pasco that might be interested on having us diagnosing your sites, please contact PI Bernardita Sallato.
Bernardita Sallato C.
WSU Tree Fruit Extension Specialist
24106 N Bunn Rd,
Prosser, WA 99350, USA
Phone: 509 4398542
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Dong, C. X., J. M. Zhou, X. H. Fan, H. Y. Wang, Z. Q. Duan, and C. Tang. 2004. Application Methods of Calcium Supplements Affect Nutrient Levels and Calcium Forms in Mature Tomato Fruits. Journal Of Plant Nutrition Vol. 27 (No. 8):1443–55.
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Marschner H. 2002. Mineral Nutrition of Higher Plants. 3rd edition. Academic Press, London, U.K
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WSDA. Specialty Crop Block Grant Awards. https://agr.wa.gov/Grants/docs/2018AwardAbstracts.pdf