BACKGROUND

Tree vigour continues to be a major concern in cherry production. Often, trees can grow in excess of 1 - 1.25 metres per year, and reach over 5 metres in height within three years. Growers currently continue to prune trees heavily to maintain the required height. Constant pruning may have severe consequences on long term production. High vigour during early growth normally delays the onset of the reproductive phase, thus delaying returns. Heavy pruning of trees can lead to diseases such as silverleaf, and also reduce the production efficiency because of extra vegetative vigour that compensates for the amount of pruning. Tree vigour may be controlled by several ways, which include use of dwarfing rootstock, use of plant growth regulators, restriction of root growth and regulated deficit irrigation.

The use of dwarfing cherry rootstocks may overcome the vigour problem. However, most breeding of dwarfing rootstocks has been conducted in the northern hemisphere and performance under southern hemisphere conditions has had to be tested. German, Italian, English and Belgian rootstocks have been evaluated at the Marlborough Research Centre since 1990.

The sweet cherry cultivar Stella was used as a scion, and the performance of the rootstocks was determined through annual extension growth, tree height, canopy area, butt circumference, and internode length. Dates of bloom and yield were also assessed, and yield efficiency was determined using canopy volume.

The following rootstocks were used in the trial: GM - 61, 79, and 9 (Gembloux); D1 and D16 (ex Oppenheim, West Germany); CAB 4D, 11E, and 6P (ex Italy); CER 10, 11, and 13 (ex Weihenstephen, West Germany); Giessen series 154 - 4, 154 - 7, 173 - 9, 148 - 8, 172 - 7, and 148 - 2; Colt; Prunus mahaleb M23. The different rootstocks were received in different years, therefore the results are comparable only within plants of the same year of planting.

RESULTS

The results of only 8 of the 19 rootstocks (Colt, CER 11, CER 13, CER 10, CAB 4D, GM 61 and 79, and Mahaleb) which were planted in 1989 are presented. With the objective of selecting a dwarfing rootstock, the evaluation sought to choose those with the highest yield efficiency, short internode length, and least height. However, other criteria may also be used to select stocks, such as flowering time and harvest time.

Five years from planting, the rootstock GM 79 is proving to be relatively the most dwarfing, followed by Mahaleb, GM 61, CER 10, CAB 4D, CER 11, CER 13, and Colt. The heights of these trees ranged from 3.8 - 5.4 m. The semi-dwarfing characters could be attributed mainly to lower canopy volume (function of height and canopy base area), shorter internode length and extension growth.

From an economic perspective, yield was highest in CER 11, followed by CER 13, GM 79, CER 10, Colt, CAB 4D, GM 61, and Mahaleb. However, yield efficiency was highest in GM 79, followed by CER 13, 11 and 10 Colt, Mahaleb, CAB 4D, and GM 61. In a commercial situation, GM 79 could perform even better at planting densities of 1,000 - 2,000 plants per hectare. In conclusion, GM 79 is considered to be the most dwarfing and production efficient rootstock so far. Although Mahaleb and GM 61 were dwarfing, their production efficiencies were comparatively low. The rootstocks CER 11 and 13 may prove to be suitable replacement for the traditional rootstocks of Mahaleb, Mazzard and Colt, in view of their high yield efficiencies and production capabilities.

These results are pertinent to the Marlborough conditions, as the performance of these rootstocks may be different in other climatic regions.

Summary Table:

Rootstock	Average growth ext. (cm)	Average butt circ. (cm)	Average canopy area (cm2)	Average internode (cm)	Total height (m)	Canopy volume (m3)	Average yield (kg)	Yield efficiency
CAB 4D	65.0	42.0	5.10	2.8	4.5	7.6	4.93	0.64
CAB 6P	66.4	27.0	6.50	3.1	3.6	7.8	7.88	1.01
CAB 11E	64.1	21.0	3.60	2.5	3.1	3.7	4.20	1.14
CER 10	63.3	44.1	6.20	2.4	4.3	8.8	7.11	0.81
CER 11	49.6	38.6	7.00	3.3	4.8	11.2	20.45	1.83
CER 13	62.9	41.7	5.2	2.6	4.7	8.1	19.50	2.42
GM 9	74.3	10.5	0.50	3.1	2.3	0.41	-	-
GM 61	64.1	32.4	2.7	2.4	4.0	3.6	2.24	0.63
GM 79	50.0	33.6	3.01	2.8	3.8	3.8	10.26	2.68
148-2	68.1	10.7	0.60	2.7	2.0	0.4	-	-
148-8	73.9	13.5	1.20	2.8	2.3	0.9	-	-
154-4	100.1	12.8	0.86	2.4	2.4	0.7	-	-
154-7	112.6	11.9	0.48	2.5	2.6	0.4	-	-
172-7	108.2	11.5	0.52	2.9	2.3	0.4	-	-
173-9	86.8	12.3	0.68	2.4	2.4	0.5	-	-
Colt	65.9	49.2	5.50	3.4	5.1	9.3	6.86	0.73
P.mahaleb	56.4	31.8	2.12	1.7	3.9	2.8	1.96	.71