Obrana doktorskog rada :: Jurica Duvnjak, mag. ing. agr.

Influence of drought stress during anthesis on agronomic and morphological traits of winter wheat and its physiological and molecular response
(Utjecaj sušnog stresa tijekom klasanja na agronomska i morfološka svojstva ozime pšenice te njezin fiziološki i molekularni odgovor)

30.4.2025. u 11:00 sati, Velika vijećnica Sveučilišta u Zagrebu Agronomskog fakulteta (VI. paviljon)

Mentori doktorskog rada:

• prof. dr. sc. Hrvoje Šarčević, Sveučilište u Zagrebu Agronomski fakultet
• dr. sc. Valentina Španić, znanstveni savjetnik, Poljoprivredni Institut Osijek

Povjerenstvo za obranu doktorskog rada:

• izv. prof. dr. sc. Ivanka Habuš Jerčić, Sveučilište u Zagrebu Agronomski fakultet
• izv. prof. dr. sc. Zorana Katanić,  Odjel za biologiju, Sveučilište Josipa Jurja Strossmayera u Osijeku
• izv. prof. dr. sc. Rosemary Vuković, Odjel za biologiju, Sveučilište Josipa Jurja Strossmayera u Osijeku

Sažetak:
Wheat (Triticum aestivum L.) is the most important cereal crop in the world. It contributes as a major source of protein and calories in the daily human diet. Wheat production is severely threatened by unfavourable climate changes, resulting in drought stress. Drought can significantly reduce wheat growth and development as well as final grain yield. Therefore, achieving a high grain yield of wheat is a challenge for breeders. In order to explore the effects of drought on different agro-morphological and physiological traits of six wheat varieties, the experiment was set up during two growing seasons (2021/2022 and 2022/2023) in field conditions, where it was not possible to isolate one stress. Therefore, a corresponding experiment was also set up in a greenhouse where drought stress was simulated at two intensities (mild and severe) by withholding watering for 45 and 65% of the volumetric soil moisture content (VSMC) for 14 days at the anthesis stage. The objectives of this research were to determine the agro-morphological and physiological response of winter wheat varieties to two intensities of drought stress at the anthesis stage and to define the expression level of genes related to drought resistance of wheat varieties.

In the field conditions, different amounts of rainfall and average temperatures during the two-year field experiment were recorded. In the first growing season, a dry period (from January to April) was recorded, but a good grain yield was achieved. Further, grain yield was significantly positively correlated with 1000 kernel weight and maximum quantum yield of primary photochemistry (TRO/ABS) at the second measurement point, coinciding with the tillering stage. Only in the highest-yielding variety Bubnjar, the TRO/ABS value was at the same significance between the second and third measurement points (tillering and stem elongation stage). In contrast to the first growing season, there was more rainfall in the second growing season (especially through April and May), which led to the occurrence of more diseases, resulting in reduced grain yield. The three highest-yielding varieties more efficiently escaped yellow rust pressure at the stem elongation stage and showed the lowest increase in TRO/ABS. In both growing seasons, variety Bubnjar had the highest grain yield and the lowest protein content.

In a greenhouse, on the 14th day after drought stress, morphological parameters were measured and flag leaves were collected to identify physio-biochemical and molecular changes. Severe drought stress led to abscisic acid (ABA) accumulation in the flag leaves and resulted in a significant decrease of chlorophyll a content in the drought sensitive variety, indicating a severe loss of photosynthetic reaction centres. The content of carotenoids, which could play an important role in resistance to drought stress, tended to increase in drought tolerant variety. Further, a significant decrease in catalase (CAT) activity was observed at mild drought stress, compared to control, in drought sensitive variety, and at severe drought stress, in all medium sensitive varieties. Drought tolerant and medium tolerant varieties responded to both drought stresses with a decrease in total glutathione (tGSH) content. The results of gene expression analysis showed that severe drought increased the levels of DHN5 and WZY2 genes in drought tolerant variety, whose grain weight, area, and length did not significantly change in maturity. On the other hand, drought sensitive and medium sensitive varieties showed the greatest decrease in grain yield-related traits. Both drought stress conditions induced variety-specific responses that depended on the severity of the drought stress. The identification of different mechanisms under drought can contribute to the selection of drought tolerant varieties. 

Ključne riječi: drought stress; grain yield; hormonal response; molecular response; physiology; photosynthesis; quality traits; winter wheat