Dried grape scion and rootstock evaluation program (DG19000)

The 2023 drying season proved to be very difficult for the dried grape industry with mild, humid conditions during the growing season which produced considerable inflorescences losses from downy mildew around flowering; a 3 week delay in fruit maturation (the latest in more than 50 years) and consequently, poor drying conditions associated with the late cutting of canes, low temperatures and significant rainfall in April (i.e. mean max 22 oC with a  total of 25 mm rainfall).  

Ten drying selections grafted on Ramsey rootstocks were evaluated in 2023. They included 5 high priority selections identified in 2022 and established in a Plant Breeders Rights (PBR) comparator trial in spring 2022; 4 selections identified with potential during the pre-harvest inspection and a selection identified previously for release to industry with PBR protection.  Unfortunately, the performance of only one of these selections was satisfactory in 2023 due, in one case, to low yield and in three cases to delayed fruit maturation compounded by very high cropping levels leading to very slow drying. In contrast, the 4 selections identified pre-harvest all reached adequate maturity levels (TSS >20 oBrix) when canes were cut between the 27th February and 14th of March. These selections produced adequate to very high yield (8.2 – 17.4 t/ha) of quality dried grapes. The results confirm the view that a number of seasons of evaluation are required before final decisions on release of new selections to industry can be made, particularly when seasonal conditions are abnormal. A PBR application for a selection with high productivity and good fruit quality under research and commercial conditions has been submitted with the name, Murray Bold. 
 
The performance of new rootstocks is undertaken in two rootstock trials established with Carina, Sultana and Sunmuscat as scions and managed with control and deficit (45% of control) irrigation treatments.  Vine performance includes assessment of fruit maturity and berry weight from pre-harvest samples and at harvest, measurement yield and bunch number and calculation of bunch weight, berries per bunch and total sugar per vine. Data analyses have shown potential to select rootstocks that have higher tolerance to water deficits than others. In 2023 the focus was on collection of comparative data for 3 high priority rootstock selections for which PBR applications have been submitted to assist with commercialisation and grower adoption. The performance of three other selections which have previously shown some promise was also undertaken. Unfortunately, one selection which has consistently produced up to 20% more crop across all three scions than the commercial rootstocks (Ramsey, 140 Ruggeri and 1103 Paulsen) has shown susceptibility to infestation by both root knot nematodes and phylloxera and hence, cannot be recommended for widespread industry adoption. The performance of the other 2 selections in 2023, compared to the commercial rootstocks and the three high priority selections already identified for naming and release did not justify their further development.  

Overall, the results continue to show that specific rootstocks may be required for different scions to optimise their performance and for most traits that rootstock performance is consistent across seasons.