Endophytic fungi promote plant growth and mitigate the adverse effects of stem rot: an example of Penicillium citrinum and Aspergillus terreus

Disease resistance is a highly desirable crop trait in the sustainable agricultural industry. Endophytic fungi with gibberellins-secreting potential are now widely known for their ability to stimulate plant growth, but their role in promoting disease resistance in plants has rarely been reported. We have studied the role of Penicillium citrinum LWL4 and Aspergillus terreus LWL5 in time-dependent manner on sunflower (Helianthus annuus L.) growth, disease resistance and their capacity for the regulation of hormone signaling networks involved in plant defense against the stem rot caused by Sclerotium rolfsii for 3, 6 and 12 days after treatment (DAT). Our results show that plant growth characteristics (i.e. shoot length, shoot diameter, shoot fresh/dry weight, transpiration, stomatal conductance, photosynthesis and chlorophyll content) were promoted in fungi-treated plants with or without the disease caused by Sclerotium rolfsii as compared to their respective controls in 3, 6 and 12 DAT. The negative impacts of stem rot in endophyte-treated diseased plants were greatly reduced in comparison to control diseased plants shown by low disease severity in 3, 6 and 12 DAT. Similarly, fungal endophytes in diseased plants relieved the biotic stress in time-dependent manner (3, 6 and 12 DAT) as shown by low level of endogenous salicylic acid and jasmonic acid contents and were significantly higher in control diseased plants. Furthermore, we observed that the Penicillium citrinum LWL4 association had a greater positive effect on sunflower plants than Aspergillus terreus LWL5. It was concluded that inoculation with fungal endophytes reprogramed plant growth during disease incidence by regulating responses associated with host plant defense. Management strategies involving endophytic symbiosis can help achieve sustainability in agriculture in an eco-friendly manner by reducing excessive fungicide use.     

Resource distribution and the trade-off between seed number and seed weight: a comparison across crop species

In grain crops, total sink capacity is usually analysed in terms of two components, seed number and individual seed weight. Seed number and potential individual seed weight are established at a similar timing, around the flowering period, and seed weight at maturity is highly correlated with the potential established earlier. It is known that, within a species, available resources during the seed set period are distributed between both yield components, resulting in a trade-off between seed number and seed weight. Here we tested if this concept could apply for interspecific comparisons, where combinations of numbers and size across species could be related to the total available resources being either allocated to more seed or larger potential individual seed weight during the seed set period. Based on this, species differences in seed weight should be related to resource availability per seed around the period when seed number is determined. Resource availability per seed was estimated as the rate of increase in aboveground biomass per seed around the period of seed set. Data from 15 crop species differing in plant growth, seed number, seed weight and seed composition were analysed from available literature. Because species differed in seed composition, seed weight was analysed following an energy requirement approach. There was an interspecific trade-off relationship between seed number per unit of land area and seed weight (r = 0.92; F(1, 13) = 32.9; n = 15; P < 0.001). Seed weight of different species was positively correlated (r = 0.90; F(1, 13) = 52.9; n = 15; P < 0.001) with resource availability per seed around the seed set period. This correlation included contrasting species like quinoa (Chenopodium quinoa; ∼100000 seeds m⁻², ∼4 mg equivalent-glucose seed⁻¹) or peanut (Arachis hypogaea; ∼800 seeds m⁻², ∼1000 mg equivalent-glucose seed⁻¹). Seed number and individual seed weight combinations across species were related and could be explained considering resource availability when plants are adjusting their seed number to the growth environment and seeds are establishing their storage capacity. Available resources around the seed set period are proportionally allocated to produce either many small seeds or few larger seeds depending on the particular species.     

Generation of white mold disease-resistant sunflower plants expressing human lysozyme gene

Sunflower plants were transformed via co-cultivation of previously bombarded hypocotyl explants with Agrobacterium tumefaciens harboring the plasmid pNGL that contains the human lysozyme gene. The transformed shoots were selected using kanamycin and regenerated plants were analyzed using histochemical β-glucuronidase assay. Southern, Western and Northern blot analyses indicated the transfer, expression and stable integration of the foreign DNA into the sunflower genome. Resistance against the phytopathogenic fungus Sclerotinia sclerotiorum, which causes white mold disease, was confirmed using a phytopathogenic test and microscopic observation of the infection process.     

Agarose embedding affects cell wall regeneration and microtubule organization in sunflower hypocotyl protoplasts

Sunflower hypocotyl protoplasts ( Helianthus annuus L. cv. Emil) divide symmetrically to form loosely associated microcolonies when cultured in liquid medium, whereas when embedded in agarose beads they divide asymmetrically to give rise to embryo-like structures. To understand the relationship between protoplast embedding and cell division patterns, we studied the deposition of β-linked glucan and the dynamics of microtubules during early phases of culture. After one day in culture, under both culture conditions, a small proportion of the protoplasts had already begun to rebuild a β-glucan cell wall and the process reached completion in all protoplasts after 10 days. Callose deposition was faster in agarose than in liquid medium but it concerned only 30–40% of the protoplasts and was not related to either division type. No marked differences were observed in cortical arrays of microtubules. However, in embedded protoplasts perinuclear microtubules formed a well-defined basket around the nucleus; these microtubules were never observed in liquid-cultured protoplasts. A narrow preprophase band was present only in dividing protoplasts cultured in liquid medium. The results suggest that asymmetric division could be related to the lack of a narrow preprophase band and that protoplast embedding enhances nucleation or stabilization of microtubules.