Priming of Citrullus lanatus var. Colocynthoides seeds in seaweed extract improved seed germination, plant growth and performance under salinity conditions

Abstract

Citrullus lanatus var. Colocynthoide ″Gurum″ is an unconventional crop that can be utilized as a new source of edible oil and has the ability to grow in a variety of harsh conditions. To mitigate the adverse effects of salinity on seed germination and plant performance of C. lanatus, seeds were primed in the aqueous extracts of the seaweed Ulva lactuca before planting under greenhouse conditions. The aqueous extract of U. lactuca at 8% w/v led to maximal seed germination percentage and seedling growth of C. lanatus. Moreover, U. lactuca extract counteracted the negative effects of salt stress on the plant by significantly increasing the activity of SOD, CAT, and POD. The bioactive components of U. lactuca, e.g. glycine betaine and phenolic compounds can account for such beneficial role of algal extract on C. lanatus. Thus, priming of C. lanatus seeds in U. lactuca extract with various concentrations of U. lactuca extract can be employed as an effective practice for successful seed germination, improved plant growth and enhanced salt resistance, probably as a result of increased antioxidant enzymes activity and photosynthetic pigments.

Introduction

Salinity is one of the widely spread agricultural problems all over the world that can severely limit crop production. It is estimated that up to 20% of the irrigated lands in worldwide are affected different extents by salinity, while 2.1% of the arid lands are suffering from salt stress, and the problem is aggravating. Salinity stress decreases plant growth by adversely affecting various physiological and biochemical processes. Salinity stress decreases photosynthesis rate with a significant reduction in the chlorophyll content which eventually resulted in reduced sunflower yield. One of the physiological changes occurring when plants are exposed to stress conditions is the enhanced production of reactive oxygen species (ROS). Excessive salt ions can exert dangerous effects like ion toxicity, osmotic stress, and nutritional imbalance, which eventually lead to decreased growth and yield. To cope with salinity stress, plants experience increased activity of antioxidant enzymes.

Seed germination is a critical developmental phase in the life cycle of plants and is a major limiting factor for establishing plants under salinity conditions. Salt stress affects percentage and rate of germination, as well as the subsequent seedling growth in different ways depending on plant species. The impact of stress arising from more than one salt on seed germination is less severe than that arising from a single salt. To overcome the impact of salt stress on plant growth and performance, seed priming can be an efficient and economical technique during the early stage of plant life. Seed priming is a process in which seeds are hydrated in different solutions of natural or synthetic compounds. Algal extracts have priming effects that can increase seed germination and plant growth under the impact of salinity and other abiotic stresses.

Algae are rich in biologically active components, that have the potential to be used as soil cleansing agents, biofertilizers, plant growth promoters and can help in soil cleansing and; fertilization, and plant protectants agents from biotic and abiotic stress factors. Due to their plentiful content of biostimulants, algae have been employed to boost plant performance and resistance to environmental stresses due to their plentiful biostimulant chemicals, plant performance, and tolerance to environmental stresses. Bioactive compounds derived from marine algae have recently been used as biofertilizers for crops to increase the magnitude and yield of agricultural and horticultural crops and quality while minimizing environmental impacts. Seaweed extracts contain a variety of growth hormones, polysaccharides, and macro- and micronutrients. The extract of the seaweed Ulva rigida improved salt stress resistance and protect plants from oxidative damage arising from abiotic stress.

Citrullus lanatus var. Colocynthoides (Gurum), family Cucurbitaceae, locally known as seed watermelon or ″Gorma″ is a promising fodder and oil crop in Egypt. The foliage of the plant is used as animal feed and its seeds have been investigated as an alternative source of vegetable oil and as a new source of high-quality pectin for commercial utilization. However, seed germination and plant growth of C. lanatus are affected adversely by salinity. Meanwhile, the use of synthetic chemicals as priming agents for seeds under stress conditions has major negative environmental concerns. Therefore, this work is conducted to overcome the negative effects of salinity on seed germination and growth of C. lanatus through seed priming in algal extracts. The study hypothesized that priming of C. lanatus in extracts of the seaweed Ulva lactuca could improve seed germination and plant growth under the impact of salinity, probably via increasing the content of photosynthetic pigments, antioxidants and other bioactive constituents.

Read more at Nature.