Cand.Biol.Sci. N.S. Kiseleva

The State Research Institution All–Russian Scientific and Research Institute of Floriculture and Subtropical Crops of the Russian Academy of Agricultural Sciences

STUDYING ORGANOGENESIS STAGES FOR ASSESSING FORMATION OF PEARS GENERATIVE POTENTIAL

Modern technologies of fruit crops cultivation aimed at obtaining high and stable yields. Currently, the average yield of fruit crops is far from potentially possible. This explains the huge dependence of farmers on "freaks" of nature, so as never before the industry has a task to manage production process in years with specific weather conditions.

The urgency of this problem stems from the fact that most modern cultivars of fruit crops having high biological productivity potential, show a lack of resistance to environmental stress, especially when the years with favorable conditions change with the years in which there are periodical stressful manifestations (spring night freezing, fogs), which reduce varietal productivity. Resolving this issue is impossible without studying the mechanisms and patterns of production process, disclosure of potential fruit plants under certain cultivation conditions, taking into account the implementation of the adaptive capacity within the effect from abiotic factors [1, 2].

Generative buds of pear cultivars with different ripening terms from the collection of the given Institute (c. Sochi) served as research objects. Buds differentiation was studied in temporary preparations (anatomic cuts), using anatomical and morphological techniques [3, 4].

In the southern fruit zone of the Black Sea coast of Krasnodar region, pears have completely enough warm, but the phases of development are unstable in terms of low and high temperatures. Low temperatures have a lot of harm in winter and spring. In spring and summer, there is usually no lack of warmth, but high summer temperatures can disrupt the development of flower buds. For example, when the average daily temperature is above 25 ⁰C, differentiation of pear flower buds stops.

The time required for the main phenological phases of seasonal development for zoned and promising pears cultivars (beginning of vegetation, beginning and the end of flowering, removable fruit ripeness), corresponding to our climatic conditions are shown in Table 1.

Table 1.

Main stages of passing phenological phases by pear trees

Cultivars	Beginning of bud opening		Beginning of flowering		Removable fruit ripeness
	dates	Т average ^0С	dates	Т average ^0С	date	Sum of active temperatures, ^0С
Early summer	11.03±8	4.4±2.5	15.04±10	9.0±3.5	7.08±9	2310…2755
Summer	17.03±9	5.0 ±1.5	20.04±11	13.8 ±4.7	21.08±10	2755…2932
Autumn-winter	24.03±11	7.0±1.5	22.04±9	15.9±5.5	1.09±15	2932…3600

Phenological observations over pear development in different areas have scientific and practical importance and are obligatory element of production and biological cultivar-studying. By terms of any particular phase it is possible to assess the degree of cultivars adaptability to growing conditions and their economic and biological value. It was noted that all the researched cultivars had a considerable variability in terms of passing development phases, which is related to the biological features of cultivars and weather conditions in different years.

According to long-term data on the average beginning of vegetation for the studied pear cultivars, in the first-third ten days of March it was recorded that the difference between early and late cultivars within a year is 6-12 days. Deviations in vegetation term reaches 7-25 days in the same cultivars, depending on the year.

The number of days of the interphase period (beginning of the vegetation - beginning of flowering) varies depending on the year from 14 to 35 days. With the increase of the average daily temperature during the interphase period, its duration sharply reduces (R = -0,77).

Referring to the beginning of flowering phase in the studied pear cultivars, there has been observed a variability, which is related to the biological features of cultivars and weather conditions. Duration of flowering by long-term average data varies from 5 to 12 days (C_V= 8,9%).

During 2002-2010 years, when meteorological data for each analyzed year were studied, in order to calculate the multivariate regression some factorial features were selected: X₁- date of beginning of the growing season; X₂ -average temperature during the beginning of flowering; Х_{3 -} sum of temperatures above 5⁰С by the beginning of flowering.

A regression equation of a standard form was obtained : Y=4,7X₁+0,9X₂-3,9X₃, where Х_{1 is a} date of the start of the growing season; X₂- average temperature during the beginning of flowering; Х_{3 —} sum of temperatures above 5⁰С by the beginning of flowering (R=0,89; R²=78%).

According to the results of dispersion analysis, we can say that climatic factors (91,94% within F_ф>F_т) affect the beginning of the growing season, and the sequence of entry into the growing season is maintained by the varietal characteristics (71,46%).

The beginning of flowering is more affected by varietal characteristics (71, 46%) than by climate (2,33%); but the yield is more effected by weather conditions (70,56%) during the flowering period than by particular cultivars (17,5% ).

The initial stage in studying pear efficiency is a research of its biological potential which is preceded by fruit buds laying and formation of generative shoots (Fig. 1)

Figure 1. Formation of generative potential at the third stage of organogenesis in pear cultivar called Chernomorskaya Yantarnaya. Increase x 480.

In order to make a microscopic study of pear organogenesis, fruit buds were selected from 2 trees of the same age for each cultivar (2-4 bouquet branches and 2-4 annual growth shoots from different sides of the tree), on bouquet branches and annual growth shoots located on the branches of fourth-fifth order of embranchment. The patterns were sampled with intervals of 2 - 12 days depending on the phase and intensity of body-forming processes, with the aim to look over.

Microscopic examination of pears organogenesis was carried out 3 weeks before flowering, when two formative processes occurred at the same time in the flowers, i.e. microsporogenesis and formation of male gametophyte, as well as and macrogenesis and formation of female gametophyte (VI - VII stages of organogenesis).

It is determined that the intensity of plant development processes during this period was controlled mainly by external factors — first of all by air temperature (Fig. 2).

a) b)

I-first –ten-day period of March; II-III- first -ten-day period of July – first -ten-day period of August; IV-second-third ten-day period of August; V-VI-VII-VIII-first-third ten-day period of April; IX-third ten-day period of March - first-second ten-day period of April; X-first-second ten-day period of June; XI- first - ten-day period of July; XII-second-third ten-day period of July.

Figure 2. Dynamics of air temperature (a) and total precipitation (b) in 2012-2013 by ten-day periods (first-third) and stages of pears organogenesis (I-XII).

Stabilization of the temperature in the range of 9-11⁰С stimulated activity in growth processes: an intensive growth of all the organs of inflorescence and floret (sepals and petals grew especially quickly, slowlier - pistils and stamens).

Since the beginning of the growing season and spring development, we studied VII-XII organogenesis stages of fruit buds development [1, 3, 4]. The formation of pollen mother cells in the anthers (VII stage) and tetrads of microspores (VIII stage) are characteristic. Formation of single-core and dual-core pollen (IX stage) coincides with the flowering period. Final stages in foundations of productivity are associated with the development and maturation of pear fruits (X-XII stages).

It was determined that in our conditions, the formation of pear potential productivity is characterized by a lack of precipitation, high temperatures and dry air and soil. Therefore, knowledge of the organogenesis stages and conditions of their passage will allow to observe formation and reduction of efficiency elements (generative shoots, flowers, fruits) on every stage, to assess the cultivar and its response to adverse environmental factors, which can be predicted and used for further work, including selection of cultivars with later flowering period.

REFERENCES

1. Alekhina Ye.M., Dolya Yu.A. Estimation of formation and implementation of cherries productivity (Methodical manual). - Krasnodar: The State Research Institution All–Russian Scientific and Research Institute of Floriculture and Subtropical Crops of the Russian Academy of Agricultural Sciences, 2013. - 29 p.

2. Zhuchenko A.A. Adaptive agricultural crop production/A.A. Zhuchenko.-Kishinev: Shtiintsa, 1999. - 231 p.

3. Isayeva I.S. Morphophysiology of fruit plants (Lecture Course MSU) / I.S. Isayeva.-M.: MSU, 1974.-134 p.

4. Isaeva I.S. Organogenesis of fruit plants / I.S.Isayeva.-M.: MSU, 1977.-32p.

5. Program and methods of studying fruit, berry and nut crops cultivars/ under red. Ye.N. Sedova and T.P. Ogoltsevoy // Orel: - Russian Research Institute of Fruit Crops Selection, 1999. - p. 608.