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5 International Scientific Online Conference DOI: https://doi.org/10.15414/2021.9788055224015

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REPRODUCTIVE DEVELOPMENT AND PHENOLOGY PECULIARITIES OF LEONID SHUGIN’S
PRECOCIOUS PERSIAN WALNUT VARIETIES
Svіtlana Los, Vladislava Shugina, Tetyana Ryzhenko
Ukrainian Research Institute of Forestry and Forest Melioration named after G.M. Vysotsky,

Kharkiv, Ukraine; E-mail.: mailto:svitlana_los@ukr.net
One of the most important characteristics of Persian walnut (Juglans regia L.) cultivars is
the peculiarities of reproductive development. When creating walnut orchards, it is advisable
to select the cultivars so that the female flowers blossoming of some of them coincide with the
time of pollen flight for others. It is believed that protogenic walnut trees are more productive.
The research aimed to determine the peculiarities of reproductive development of
precocious Persian walnut cultivars obtained by Leonid Shugin.
Phenological observations of 27 cultivars were carried out every 7–10 days from May to
September 2020 and 2021. The studied cultivars are precocious and are represented by hybrids
of several generations from crosses of Uzbek precocious Kalmykov’s cultivars with local frost-
resistant precocious forms and Kocherzhenko’s precocious cultivars, as well as with Sadko’s
lateral fast-growing ones. Reproductive development of female (♀), male (♂) and bisexual
(♀♂) inflorescences was assessed on a 5-point scale. The type of dichogamy and the presence
of secondary flowering were determined.
The analysis of the obtained data showed that half of the examined cultivars (54 %) are
protogenic, a third (32 %) are homogamous and only 14 % are protandric. Despite the
significant differences in weather conditions in 2020 and 2021, the beginning of flowering of
both ♀ and ♂ inflorescences in most cultivars was fixed in the late first decade of May. At the
same time, flowering in cooler conditions in 2021 was several days longer. One week after the
end of the first flowering, the appearance of secondary inflorescences was noted in some
cultivars. Both years in a row, the beginning of secondary flowering occurred in the late third
decade of May. The number of trees with secondary male flowering was slightly higher than
with the female one. Secondary flowering was noted for 70.3 % of observed cultivars.
10 cultivars are forming secondary bisexual inflorescences (female flowers at the base,
male flowers at the top, and bisexual flowers in the middle part of the inflorescence), in
particular the 'Sadko', 'Bomba', 'Bagryany', 'Petliura', 'Turnyk', 'Shukhevych' cultivars. Three
cultivars form a significant number of such inflorescences throughout the summer, even in
early September. Some researchers consider such manifestations to be developmental
abnormalities. On some trees, secondary inflorescences are observed annually, and on others –
only as an episodic phenomenon. Our research shows that each cultivar is characterized by the
formation of certain types of inflorescences in certain periods of vegetation, but the intensity of
their formation varies in different years.
Secondary inflorescences are formed on shoot tops from axils buds. We can assume that
these buds are not dipped dormant until the spring of next year, as is the case with classic
cultivars, and continue to develop, forming shoots with inflorescences. Their number to a
certain extent depends on the number of ovaries formed from the first flowering. When the
number of ovaries is small, secondary flowering is more abundant. Probably the secondary
flowering is a kind of adaptive mechanism that promotes the formation of fruit yields in adverse
conditions of the growing season.
Thus secondary flowering is a fairly common phenomenon among the Shugin’s walnut
cultivars. Features of their reproductive biology, in particular the phenomena of secondary
flowering and precocious, require more detailed study and application in further breeding.

Keywords: phenology, dichogamy, secondary flowering, precocious.

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