Nanoparticle-Mediated Seed Priming Improves Germination, Growth, Yield, and Quality of Watermelons (Citrullus lanatus) at multi-locations in Texas

Abstract

Seed priming uses treatments to improve seed germination and thus potentially increase growth and yield. Low-cost, environmentally friendly, effective seed treatment remain to be optimized and tested for high-value specialty crop like watermelon (Citrullus lanatus) in multi-locations. This remains a particularly acute problem for triploids, which produce desirable seedless watermelons, but show low germination rates. In the present study, turmeric oil nanoemulsions (TNE) and silver nanoparticles (AgNPs) synthesized from agro-industrial byproducts were used as nanopriming agents for diploid (Riverside) and triploid (Maxima) watermelon seeds. Internalization of nanomaterials was confirmed by neutron activation analysis, transmission electron microscopy, and gas chromatography-mass spectrometry. The seedling emergence rate at 14 days after sowing was significantly higher in AgNP-treated triploid seeds compared to other treatments. Soluble sugar (glucose and fructose) contents were enhanced during germination in the AgNP-treated seeds at 96 h. Seedlings grown in the greenhouse were transplanted at four locations in Texas: Edinburg, Pecos, Grapeland, and Snook in 2017. At Snook, higher yield 31.6% and 35.6% compared to control were observed in AgNP-treated Riverside and Maxima watermelons, respectively. To validate the first-year results, treated and untreated seeds of both cultivars were sown in Weslaco, Texas in 2018. While seed emegence and stand establishments were enhanced by seed priming, total phenolics radical-scavenging activities, and macro- and microelements in the watermelon fruits were not significantly different from the control. The results of the present study demonstracted that seed priming with AgNPs can enhance seed germination, growth, and yield while maintaining fruit quality through an eco-friendly and sustainable nanotechnological approach.

Figure 1

TEM images of silver nanoparticles showing the morphology of synthesized silver nanoparticles at (A) scale bar 100 nm (B) scale bar 200 nm, (C) X-ray diffraction pattern of silver nanoparticles synthesized using onion peel extract.

Figure 2

Effect of nanoparticle treatment on diploid (Riverside) and triploid (Maxima) watermelon seeds up to 96 h. Rapid degradation of polysaccharides and disaccharides in nanoparticle-treated samples shown at different time points. Control is unprimed, TNE is turmeric oil nanoemulsion and AgNPs is silver nanoparticles. Values are mean ± SEM (n = 6).

Figure 3

Effect of nanoparticle treatments on chlorophyll content, stem diameter and shoot length in watermelon seedlings at 21 days after transplanting. (A) Chlorophyll a (Chl a) and (B) chlorophyll b (Chl b) content in Riverside and Maxima watermelon seedlings at 21 days after sowing (DAS). Boxplots show the shoot length of watermelon grown in (C) first year, 2017 and (D) second year, 2018; stem diameter of watermelon grown in (E) first year, 2017 and (F) second year, 2018. Control is unprimed, TNE is turmeric oil nanoemulsion and AgNPs is silver nanoparticle-treated watermelon seedlings. *Denotes statistical differences between treatments at the 5% level according to t test and ‘×’ denotes mean.

Figure 4

Effect of seed priming with turmeric nanoemulsion and silver nanoparticles on the germination, seedling growth and vine development of diploid (Riverside) and triploid (Maxima) watermelon varieties, compared with unprimed control.

Figure 5

Effects of nanoparticles on the growth parameters at 40-day-old watermelon plants and yield. (A) Vine length (cm) of Riverside, (B) vine length (cm) of Maxima, (C) vine thickness (mm) of Riverside, and (D) vine thickness (mm) of Maxima watermelon plants grown in five locations of Texas (Snook, Grapeland, Edinburg, Pecos, and Weslaco). (E) Effect of nanopriming on yield of watermelon grown in three locations in Texas (Snook, Grapeland and Weslaco). Watermelons were harvested three times during the first year at Snook and Grapeland. Due to bad weather conditions, a single harvesting was done in Weslaco. Control is unprimed, TNE is turmeric oil nanoemulsion and AgNPs is silver nanoparticles treated watermelon. Different letters denote significant difference (p ≤ 0.05) between treatments. Data represent mean ± SEM.

Figure 6

Transmission electron microscopy (TEM) images of internalization of silver nanoparticles in the (A) unprimed triploid (Maxima) seed, (B) AgNP-primed Maxima seed (C) unprimed Riverside seed and (D) AgNP-primed Riverside seed. Arrows indicate regions where AgNPs (dark bead like structures) have accumulated in treated seeds.

Figure 7

Nanopriming effects on (A) Total Phenolics and (B) Radical scavenging activity of watermelon fruit; Riverside and Maxima by DPPH method. T1: unprimed, T2: turmeric oil nanoemulsion and T3: silver nanoparticles. Data are presented as means ± SEM (n = 12). Means denoted by the different letters are significantly different at (p ≤ 0.05).