- Author: Therese Kapaun
- Author: Elizabeth Fichtner
Recently, severe root rot and mortality was observed on young potted pistachio rootstock trees housed in a research plot in California. Dr. Elizabeth Fichtner, UCCE Tulare County and Dr. Cheryl Blomquist, California Department of Food and Agriculture found a new Oomycete, Phytopythium helicoides associated with the observed root rot and mortality. Phytopythium is a newly designated genus exhibiting characteristics similar to both Phytophthora and Pythium and is considered to be an evolutionary intermediary between the two genera. In collaboration with Dr. Greg Browne, USDA-ARS, and Dr. Blomquist, studies are underway in a greenhouse at the Lindcove Research and Extension Center to determine pathogenicity of P. helicoides to UCB1 pistachio rootstock.
This week at Lindcove REC the John Deere Company installed two John Deere Field Connect™ soil moisture systems in two of our mandarin research plots. The systems were donated to Dr. Mikeal Roose of UC Riverside (Dept. of Botany and Plant Science) for use in his citrus rootstock trials that are based both here and at the UC Riverside campus.
The soil moisture probe takes a reading every 30 minutes and transmits the data through either cellular or satellite communication to a dedicated website every two hours where the information can be securely reviewed from the internet. The soil moisture probe installed here has sensors at depths of 4, 8, 12, 20, and 40 inches. The system allows us to see the depth of an irrigation water application, understand where the active root zone is, and allows us to capture observations in the field through notes on the graphs. The photo below shows Technical Service Manager Craig Hornung of the Visalia John Deere office installing one of the sensors in between two Nules clementine trees. The next photo shows a sample screenshot of the data from the system installed at the UC Riverside rootstock field trial.
Pummelo (Citrus maxima) is one of several ancient lineages of citrus thought to have originated in China. Modern hybridizations of pummelo with orange have resulted in what we know today as grapefruit (Citrus paradisi), however there are many varieties of pummelo that are great tasting on their own, and in addition they tend to lack the bitterness of grapefruit. Pummelo and grapefruit have the ability to grow into enormous trees, so be careful when deciding where to plant these trees in urban settings. The largest tree at Lindcove REC is also one of the oldest, a Brown Marsh grapefruit planted in 1963 on Troyer rootstock.
Today the Citrus Clonal Protection Program (CCPP) used the Fruit Quality Lab at Lindcove REC to test several varieties of pummelo to determine whether they would be palatable and thus harvestable for the early season market. Three varieties stood out as clear taste-winners, these are Mato Buntan, Thong Dee, and Tahitian. In terms of °Brix, Mato Buntan was 10.9, Thong Dee was 11.1, and Tahitian was 11.5. As for percent acid, Mato Buntan was 0.46, Thong Dee was 0.89, and Tahitian was 0.91. Thong Dee was regarded by the ad hoc volunteer taste panel as having the best tasting juice. These three varieties will be retested every two weeks for a number of months to determine the timing and duration of "good flavor".
Fruit quality data for many varieties of citrus can be found on the websites of both CCPP and the Citrus Variety Collection (CVC), both organizations are based in Riverside, California. Their websites are as follows:
- Author: Therese Kapaun
- Contributor: Rachel Rattner
The Lane Late navel block at Lindcove was planted in 1991 and consists of 230 trees on 29 different rootstocks. Rachel Rattner is a PhD student at UC Riverside working with Dr. Mikeal Roose in the Dept. of Botany and Plant Sciences. She is investigating the impact of small RNA molecules on fruit quality. Small RNAs are naturally found in plants, and their role is to regulate the expression of genes during citrus development. Small RNAs are a recent area of study in plants and have been shown to be important in plant development, as well as in vital processes such as nutrient uptake and responses to environmental stresses. There is evidence that some of these molecules may be species-specific and can move from shoots to roots and vice versa. Therefore, small RNAs produced in different varieties of citrus rootstocks may regulate gene expression, and ultimately fruit quality, in the scion. The results from this project will be useful to citrus breeders in the future.
Rachel is sampling Lane Late navels at Lindcove REC for her project. In this photo Rachel is being assisted by Claire Federici (Staff Research Associate at UC Riverside) and is slicing immature fruit and separating juice vesicles from the segment walls. These vesicles are quickly frozen on dry ice in the field to preserve the integrity and current state of the RNA molecules present at the time of slicing.
Rootstock selection is an important component of commercial citrus production worldwide. Soil type, scion compatibility, mineral tolerance, disease tolerance, and growth traits are the primary concerns when choosing a rootstock type.
Hybrid species of trifoliate rootstocks are popular with growers in California's San Joaquin Valley. Carrizo and C-35 are two of the most common varieties for oranges and mandarins. Both share the same scientific name, Citroncirus hybrid sp.
Many of the research plots at Lindcove REC utilize the common commercial varieties of both scion and rootstock, for example Parent navel on C-35, or Nules clementine on Carrizo. This allows the results of experiments to more closely resemble actual fruit production that comprises a hefty share of the domestic and overseas markets.
This month the staff at Lindcove REC are transplanting rootstock seedlings grown in cone flats to larger pots. The seedlings will grow quickly during the fall and will be large and healthy for budding next March.