Creation of triploid grades opens a new era in apple-tree selection

The history of selection of an apple-tree at polyploidy level refers us to the thirties-fourties years of last century when the Swedish researcher Nilsson-Ehle was keen on idea of getting triploid grades by crossover of diploidic grades with tetraploid ones [12-14]. In the work [10] for the first time it was shown that among seedlings from an open pollination of diploidic widely known grades Delishes, Mutsu, Kortland and Mekintosh it is possible to select 0,3% of triploid seedlings, whereas about 25% of industrial grades of the USA of that time were spontaneous triploids. This circumstance allowed making the important conclusion that triploid seedlings in the selection relation are the most valuable ones [11]. By 1943 already were known tetraploid spontaneous sports of grades Mekintosh, Ontario, Papirovka and Uelsi. From the crossover of tetraploid grades with the diploid ones drew the big interest of triploid seedlings was got. The prospect of selection of an apple-tree at polyploidy level already then laid significant stress on. It was noted even that the development of this line should be considered as the entry into a new era of selection of an apple-tree [9-10]. The Indian scientists [15] consider that a triploidiy - an optimum level of a polyploidy at which the apple-tree shows the most economically valuable characteristics. Triploid grades arisen spontaneously or got from the crossover of two diploidic grades as a result of emergence of unreduced gametes, gained an industrial distribution (Baldwin, Gala, Dzhonagold, Mutsu, Spartan, Spigold, Jupiter, etc.). However the attention to the gaining triploid grades by the crossover of tetraploid grades and forms with diploidic arrangement of chromosomes gradually fell. We do not know triploid grades got from goal-seeking crossovers from different chromosomal forms of the types a diploid x tetraploid or a tetraploid x diploid before 2002.

In our opinion, the reason for it is that from such crossovers it is much more difficult to get the necessary volume of hybrid seedlings for selection, besides the range of tetraploid grades and forms is limited.

Carrying out researches we were guided by the standard programs and techniques [3, 4].

Results

The selection of an apple-tree on polyploidy level in the ARRIHCS started in 1970 [6]. Since 1985 the group of plant breeders of the North-Caucasian R&D of horticulture and winegrowing performed this work. Now such selection of an apple-tree is conducted also in the R&D establishment of horticulture of Siberia n.a. M.A.Lisavenko (The Gorno-Altaysk research farm) and at Sverdlovsk plant breeding station of horticulture [1].

Initial forms (donors of diploidic gametes). Almost everything spontaneously arisen tetraploid forms of known grades of an apple-tree — diploidic and tetraploid chimeras. It is caused by that apical meristem points of growth of an apple-tree consist of three histogenetic layers of cages. In the first layer (external) — epidermis, in the second (subepidermal) — a number of tissues, including both a palisade parenchyma of leaves and maternal cages of megaspore and microspore, a third layer — internal tissues. Only if the subepidermal layer is tetraploid (4х), a diploidic and tetraploid chimera acts during selection as real tetraploid and in hybrid kid from crossover with diploidic grades gives triploid seedlings. It is possible to get homogeneous tetraploid plants causing springs from internal tissues.

Along with identification of known spontaneous tetraploid grades, induction of tetraploid represents considerable attention with the help of colchicine, appiol or neutron beams.

Tetraploid trees are often characterized by a slow growth, a rare krone, incrassate springs. Fruits of tetraploid grade of an apple-tree are characterized by greater dimensions, more flattened form than thier diploidic analog, often with obviously expressed edges. Tetraploid apple-trees have the high self-fertility which can provide good setting even in adverse weather conditions for flowering. The use in hybridization of tetraploid forms of an apple-tree gives new opportunities for creation of grades with a high self-fertility [5].

As a rule, tetraploid grades of an apple-tree are not suitable for a direct practical use because of roughness of pulp and insufficiently good taste of fruits, but are of interest as an initial material in selection at polyploidy level [8].

At the ARRIHCS by the selection way new donors of diploidic gametes were created. From the crossover of Uelsi tetraploid x Papirovka tetraploid are got 10 homogeneous tetraploid forms, Uelsi tetraploid x Antonovka common — three homogeneous and tetraploid forms, from Liberti x 13-6-106 { Suvorovec— open pollination) - one form and one homogeneous tetraploid form from free pollination of Uelsi tetraploid and Suvorovec diploidic. All these forms serve as perspective donors of diploidic gametes.

During recent years in heteroploid crossover are included the new tetraploid forms got in the ARRIHCS as a result of implementation of the selection program with the use of polyploids. These are forms 13-6-106 (seedling of the grade Suvorovec), 25-35-121 (Uelsi, 4хх Panirovka, 4х), 25-37-45 (Orlovsky garland x Uelsi, 4х), 25-37-47 (SR0523 x Antonovka plain, 4х) and form 30-47-88 (Liberti, 2хх 13-6-106,4х). The particular interest is represented by the form 30-47-88 as due to its origin it has in its genome Vf gene from Liberti parent immune grade. Therefore the kid got with its participation, will possess such valuable characteristic as immunity to a scab. The harvest of triploid seedlings in hybrid kid is in average 70,5%. Besides, the tetraploid form 30-47-88 is characterized with high economic useful indexes and belongs to elite.

It is stated that tetraploid clones of grades, as a rule, significantly differ from theirinitial diploidic analogs by the size and a form of a leaf plate, the weight and the form of fruits. So, at tetraploid grade Antonovka plain (clone of Anktonovka common) fruits are larger, have more flat form which is proved by indexes of a form of fruits. Similar differences have fruits of tetraploid Uelsi comparing with initial form of diploid Uelsi.

The total amount of hybridization with the purpose of selection at polyploid level at the ARRIHCS for 42 years made 638 925 flowers on 447 combinations of crossovers. From hybridization 119 311 seeds are got and 46 897 annual seedlings are grown up.

It is established that for mass receiving of triploidiy seedlings the most perspective crossovers are of type 2x x 4х and 4х x 2х (69,5% and 55,1% of triploidiy seedlings in the kid) [7].

For the last 25 years at the ARRIHCS together with NCR&DHW from crossovers of different chromosomes created more than 20 triploidiy grades. From them allowed to using Augusta, Bezhin meadow, Darena, Maslovsky, Orlovsky partisan and Apple Spas are already included in State Register of selection achievements of the Russian Federation. Also four triploid grades (Nizkorosloe, Memory to Semakin, Rozhdestvenskoe, Jubiljar), got from the crossover of diploidic grades as a result of formation of unreduced gametes at one of parental grades, are zoned.

In 2013 the ARRIHCS recommends to inclusde in the state test two triploidiy grades Prazdnichnoe and Vavilovskoe.

The Prazdnichnoe it is got from hybridization of Prima x Dzhayent Spay. The fruits weighing 152 g (above average), of attractive appearance (4, 5 points) and nice taste (4, 3 points). The consumer period of the fruits lasts till the end of December. The grade is characterized with the high productivity (27 t/hectare), regular fructification, an immunity to a scab (Vf gene).

Vavilovskoe [18-53-22 ( Skryzhapel x OR18T13) x Uelsi tetraploid] is characterized with high (26 t/hectare) and regular productivity, immunity to a scab (Vf gene). Fruits with high commercial (the mass of 170 g) and consumer qualities. They can be stored in the refrigerator before the beginning of March.

In 2013 for high economic qualities the grades, which undergo State tests, it is offered to include Alexander Boyko, Osipovskoye and the Patriot in the State registry of selection achievements of the Russian Federation, they are also allowed to using in Central Chernozem region.

There is a positive experience of triploid grades of an apple-tree creation in the Urals.

In 1983-1987 at Sverdlovsk plant breeding station of horticulture small-fruited winterhardy grades were pollinated with the pollen of tetraploid forms from the ARRIHCS, encouraging results are received. L.A.Kotov — an originator of this initiation, considers that the polyploidy in selection of an apple-tree is especially important for regions of pioneer horticulture as this allows already in the first hybrid generation from a half-cultures and crab apples getting a large-fruited kid, by this sharply accelerating selection process [1, 2].

From triploid grades only Nizkorosloe (130 g) was slightly less in the mass of fruits than diploid control ones, other grades even surpassed Antonovka common (140 g) and Sinap Orlovsky (150 g). The special large-fruitiness characterizes a triploid grade Patriot (230 g).

The high value of grades and donor forms of diploid gametes is confirmed by the new created for the last years valuable triploid regularly fructifying grades of the ARRIHCS and the NCR&DHW.

So, with tetraploid Papirovka participation eight new grades are already got: Augusta { Orlik x Papirovka tetraploid), Daryona { Melba x Papikrovka tetraploid), Zhlinskeo, Maslovskoye, Union, Spasskoye, Apple Spas { Redfri x Papirovka tetkraploid) (the ARRIHCS and the NCR&DHW), Osipovskoye (Mantet x Papirovka tetraploid).

With the participation of tetraploid Uelsi five new grades are created: Alexander Boyko (Prima x Uelsi tetrakploidny); Bezhin meadow (Northern Sinap x Uelsi tetkraploid); Minister Kiselyov (Chistotel x Uelsi tetraploid); Fontanel ( Uelsi tetraploid x Bessemyanka Michurinsk); Turgenevskoye [18-53-22 (Skryzhapel x OR18T13) x Uelsi tetraploid].

The particular interest represents the combination in one genotype of a triploid set of chromosomes (Зх) and immunity to a scab (Vf gene). At institute seven such grades, including five from crossovers of different chromosomes are got: Alexander Boyko, Zhilinskoye, Maslovskoye, Spasskoye, Apple Spas, two triploid immune to a grade scab (Rozhdestvenskoe and Jubiljar) - from crossover of diploid grades. Grades Maslovsky, Apple Spas, Rozhdestvenskoe and Jubiljar are already included in the State registry of selection achievements of the Russian Federation allowed to using.

According to our last data, under hybridization at polyploidy level were got 2,3 times less seeds and 4,7 times less grown up annual seedlings in relation to the pollinated flowers, than under the hybridization at diploidic level. However the selection value of the seedlings created from hybridization at polyploidy level was much higher what the following data testify. Under hybridization at diploid level for allocation of one elite seedling it was necessary to grow up on the average 4121 seedlings, and on the polyploidy level - 778; for creation of one grade, sending to the state test at diploid level, on the average 86,6 thousand flowers were pollinated and 16,7 thousand annual seedlings were grown, and at polyploid level - only 46,2 thousand flowers and 2,9 thousand annual seedlings (almost six times less).

In separate combinations of crossovers at polyploid level during a grade creation still lesser volume of hybridization and cultivation of hybrid seedlings was needed. So, the grade Bezhin meadow is got in a family Northern Sinap x Uelsi tetraploid from a hybridization of 13,2 thousand flowers and only from 709 seedlings, Augusta (Orlik x Papirovka tetraploid) — from hybridization of 8,5 thousand flowers and is allocated in a family consisting of 912 seedlings.

The accurate constant distinctions according to the content of biologically active agents in fruits of triploid and diploid grades were not discovered. But it is necessary to note the high content of R-active agents in fruits of triploid grades Turgenevskoye - 482 mg / 100, Memory to Semakin - 501 mg / 100 and Augusta — 472 mg / 100 and the raised content of ascorbic acid in the fruits of a triploid grade Nizkorosloe — 18,0 mg / 100.

Thus, new triploid grades of an apple-tree are characterized by the increased mass of fruits. The average mass of fruits of eighteen triploid grades selected by the ARRIHCS makes 174 g, whereas the average mass of fruits of the best diploid grades is only 136 g. The difference is proved statistically. The majority of triploid grades according to the presence of sugars, R-active agents, ascorbic acid is not worse than diploid ones, and some such grades — are considerably better. According o the quality of fruits taste many triploid grades it are better than diploidic.

The great prospect of creation of triploid grades of an apple-tree from crossover of diploid forms with tetraploid, expected by the famous Swedish researchers in the fourties-fifties years of last century, is confirmed on practice.