Below is some info I collected about Krymsk 1 from various sources. @fruitnut reported incompatibility issues with some apricots. I think he has most experience with growing apricots on K1. This spring I grafted five apricot varieties on one K1 rootstock and 4 out of 5 took. They seem to be growing ok. I mostly used K1 for E. plums and A. plums and so far it seem to be a very good fit. With peaches/nects on K1 I had about 50% success rate, so Redhaven interstem would be advisable.
Maas et al.: Krymsk 1 (Prunus tomentosa × Prunus cerasifera) was selected by Gennady Eremin at the Krymsk Breeding Station in Russia in 1966. In comparison to St. Julien A on many European Plum cultivars, trees on Krymsk 1 were by far the least vigorous, most precocious, and most production efficient.
Bay Laurel: Dwarfing rootstock for peaches, plums, apricots and nectarines. Produces a tree about half the size of standard, roughly eight to fourteen feet. Does very well in heavy soils.
gb-online.co.uk: A semi dwarfing that grows to approx 2-2.5 m tall, comes into fruiting very early with high production. More suited for heavy soils and winter hardy.
anfic.com.au: Cold tolerant, drought tolerant, waterlogging tolerant. Looks very good in the trials for peach, plum, nectarine, and apricots. Dwarfing at least 50%. Fruit size is very good - better than Lovell on young trees. Some incompatibilities are reported in Spain with low chill nectarines. We have never seen any incompatibilities. Adaptable to many soil types including heavy soil. It does not resist stress well and can have a problem with transplant shock if not handled well. Requires good irrigation practices or the trees will be very dwarf. Seems susceptible to Pseudomonas. Good yield efficiency. Reports from California: Very good enhancement of fruit size; apricots have a good balance of renewal growth; larger fruit of Japanese plums compared to Citation. Reports from Holland: 60% of full tree size for plums; increased fruit size; less dwarf with plum than peach; could be the best apricot rootstock, check compatibility but it occurs early; susceptible to bacterial canker (although never seen in the field); some resistance to nematodes.
2002 NC-140 Peach Rootstock Trial at Geneva: Krymsk 1 (along with Controller 5) showed the greatest survival rate and the greatest percentage of functional canopy.
UC Fruit Report: In NC-140 trials with Redhaven, Krymsk 1 has been very impressive - healthy looking dwarf trees with little suckering, good production and large fruit size. Compatability with Redhaven has always been good. However, many other California varieties have been grafted on Krymsk 1 and many of these show signs of poor compatability. A report from Spain also indicated compatability problems with some varieties. Anchorage: Good, Rootknot Nematode Susceptible; Lesion Nematode: Resistant or tolerant; Ring Nematode: Susceptible; Bacterial Canker: Susceptible, Crown Gall: Susceptible.
Gerard Poldervaart: Krymsk 1 (VVA-1, P. tomentosa x P. ceracifera) is compatible with dessert and culinary plums, apricots, peaches and nectarines. In Europe, it is mainly used for plums. Trees grow very weakly on VVA-1 and their productivity is very high. The fruit size on VVA-1 is typically better than on St-Julien A or similar rootstocks. However, trees on VVA-1 can easily carry too many fruit, and therefore thinning is needed to achieve good fruit size. In dry conditions, trees on VVA-1 often grow too weakly. In most cases, an effective water supply is an absolute necessity for trees on VVA-1. Trials in Europe show that VVA-1 is very compatible with almost all varieties of dessert and culinary plums.
Fruitnut: Graft incompatibility of Montrose apricot on Krymsk 1 (reported July 2016).