Tree evaluations at the three trial locations (1) SWFREC, (2) Hendry County – Duda & Sons, and (3) Polk County – Peace River Packing Co. were continued during the fourth quarter of 2019. Tree evaluations included monthly (SWFREC) or bimonthly (Hendry County and Polk County) root growth measurements using rhizotrons and leaf flush ratings as well as biannual tree/canopy size and trunk diameter measurements.
The SFWREC field trial was terminated after 2 years of growth following a final horticultural assessment. A subset of 72 trees was excavated over a period of 3 weeks using compressed air (Airspade), which allows the fibrous roots to remain intact. A detailed analysis of the root architectures, including the number and length of lateral roots and size distribution of roots, was conducted to investigate potential differences among propagation methods and rootstocks, but also between bed side and swale side. Differences among different propagation methods were statistically significant only for the length per lateral root which was highest for rootstocks propagated from seed. Significant differences were also found among rootstock cultivars for the primary root diameters which was largest for US-802 and US-942 and smallest for US-897, US-1516, and Swingle. A trend for a larger number of primary roots and primary root length on cuttings propagated roots was observed. For many of the measured root variables significant differences were also observed between swale side and bed side. Roots growing into the bed side were more numerous, longer, and thinner compared with roots growing into the swale side. Information from these excavations will be presented during the 2019 Citrus Show in Fort Pierce.
The fourth field trial was established in November at the Florida Center for Sustainable Agriculture in Vero Beach (collaborator: Mr. Bob Adair). This trial includes the 3 rootstock varieties US-942, US-812, and US-1516, which was modified from the originally proposed cultivars (US-802, US-897, Swingle) which were not available as tissue culture propagated rootstocks. All rootstocks were propagated by seed, cuttings, and tissue culture. Therefore, the design was a 3 x 3 design, including 3 propagation methods and 3 rootstocks. For each combination 12 grafted trees were available, which were arranged in 6 replicates of 2. The scion cultivar is Valencia. Baseline tree measurements were conducted immediately after planting. Two weeks after planting, rhizotrons were inserted next to one of each of the trees in each replicate.