Posted by: HortAlaska | October 27, 2019

Microstructural and lignin characteristics in herbaceous peony cultivars with different stem strengths

These authors conducted experiments with stem strength on 8 cultivars of Chinese peonies, P. lacitflora. They were interested in learning if lignin and/or cellulose were the main components of stem strength (lignin won). In a previous article, they found that stem strength could be significantly improved by spraying plants with silicon or nano Calcium carbonate. In this study they tested 8 cultivars that had different stem strength qualities, four with poor stem strength where the stem could not hold up the fully opened flower, and four with great stems:

Screen Shot 2019-10-27 at 1.53.29 PM

We have all seen this in peony fields. I think the cultivar that could easily top the list of strong stems in my research plots is ‘Sarah Bernhardt’, but we have all seen the wimps that simply do not hold up even in a vase.

The authors measured stem diameter and length and concluded that stem diameter was a great indicator of stem strength, whereas there was no correlation with stem length. My first question was, “Where did they measure diameter?” It’s not really clear. They mention sampling the top 12 cm of the stems, but I’m not sure if it was close to the bud where the stem naturally flares or further down. The stem diameter for the top row of cultivars ranged from 3.6 mm to 4.6 mm (+ about 0.4 mm). The cultivars on the bottom row ranged from 2.7 to 3.0 mm diameter. Wow– that’s not much of a difference between the smallest (3.6mm) diameter on a straight stem and the largest (3.0 mm) diameter on a cultivar bent nearly in half!  Hm! There was a bigger difference in digital force measurements  to test mechanical strength. The top row ranged from 16.4 to 21.9 Newtons mechanical strength whereas the bottom row was 6.9 – 9.7N.

Dr, Mingchu Zhang (University of Alaska Fairbanks) and I have done a bit of work on measuring stem strength in peonies, and we have found that there are so many variables, it is difficult to pinpoint one overriding factor. Obviously, from this study, anything that can increase lignin deposition in cell walls will be beneficial. How does that translate to a grower? Not sure yet. We do know water stress, nutrient stress and growth rate all impact stem strength. So dues the cultivar, but also the “pecking order” of the buds. Even within one plant, the first buds to emerge are usually the strongest, but as nutrient reserves are used up, the buds that appear later in the season can be very weak. It is definitely worth looking at Calcium carbonate or silicon as a supplement to promote stronger stems, but I think there will always be a few wimps at the end of the season.

Daqiu Zhao, Wenbo Shi, Xing Xia, Yuhan Tang, Jun Tao⁎Jiangsu Key Laboratory of Crop Genetics and Physiology, College of Horticulture and Plant Protection, Yangzhou University, Yangzhou, 225009, PR China ABSTRACTStraight stems are highly important to herbaceous peony (Paeonia lactifloraPall.) cutflowers. To clarify whetherthe microstructural and lignin characteristics are associated withP. lactiflorastem mechanical strength, eightcultivars were used to study their anatomical structure, secondary cell wall, lignin deposition, lignin content andstructure, lignin biosynthetic enzyme activity and related gene expression levels. The results showed that stemdiameter was a direct indicator estimating its mechanical strength. Simultaneously, the number of vascularbundles, area of vascular bundles, number of duct perforations, ratio of xylem to cross-section and thickness ofsecondary cell wall had significant positive correlations with stem mechanical strength. Moreover, three ligninmonomers were all detected in the stem, and the contents of S-lignin, G-lignin and total lignin in high stemmechanical strength cultivars were higher than those in low stem mechanical strength cultivars as a whole, andlignin was deposited in the cell walls of the sclerenchyma, vascular bundle sheath and duct. Additionally, cin-namate 4-hydroxylase (C4H), cinnamyl alcohol dehydrogenase (CAD) and polyphenol oxidase (PPO) activities inhigh stem mechanical strength cultivars were higher than those in low stem mechanical strength cultivars as awhole, andCADmight be the key gene among detected lignin biosynthetic genes. Consequently, microstructuraland lignin characteristics were closely correlated with stem mechanical strength inP. lactiflora. These resultswould provide useful information concerning the physiological mechanism of stem strength. Postharvest Biology and Technology 159 (2020) 1110430925-5214/ © 2019 Published by Elsevier B.V.T

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