Triticeae Genomics and Genetics, 2025, Vol.16, No.2, 79-91 http://cropscipublisher.com/index.php/tgg 83 in growth and ended up reaching normal height by maturity. The researchers think that perhaps producing both antifungal proteins at high levels in very young seedlings might have a small metabolic cost or effect on cell elongation early on, but the plants adjust later on (maybe as their photosynthetic capacity increases, they compensate). Ultimately, these dual-gene plants maintained normal adult height and development. Across all the transgenic lines observed, there were no significant adverse growth traits. The plants went through seedling, vegetative, and reproductive stages normally. There were no deformities, no obvious stunting (beyond the tiny temporary differences noted), and they produced heads and seeds normally. This contrasts with some reports from other systems where overexpressing certain resistance genes caused unintended effects like stunted growth or early senescence (for example, some plants engineered for strong resistance show “lesion mimic” or leaf tip necrosis phenotypes as mentioned). In one reference, certain transgenic crops with heightened resistance showed growth inhibition or premature aging (like the leaf tip necrosis from Lr34 in wheat or other R genes triggering mild autoimmunity) (Horvath et al., 2001). However, in our transgenic barley lines expressing chitinase and the AMP, such issues were minimal to non-existent. Aside from the minor leaf tip necrosis in a few cases (which was very limited and occurred late in development), the plants looked and grew like normal barley. In summary, the introduction of the antifungal protein genes did not disrupt barley’s normal growth and development in any meaningful way. The transgenic barley was able to grow just as well as the non-transgenic barley under the same conditions, which is a crucial consideration for practical use. 6.2 Yield traits Yield is a critical factor for any crop - farmers and breeders will not adopt a new variety, no matter how disease-resistant, if it significantly lowers their yield. So the study also evaluated the yield components of the transgenic barley lines: things like number of ears per plant, number of grains per ear, thousand-grain weight (a common measure of grain size), and total grain yield per plant (or per plot). At maturity, they found that most transgenic lines had yield traits not significantly different from the control. In some transgenic lines, there was a slight increase in the number of effective ears (spikes) per plant compared to the control. This could be attributed to better tiller survival or more tillers due to enhanced health (less disease means the plant can support more tillers to maturity). Consequently, those lines with more ears had slightly more grains per plant than the control as well. This suggests a possible indirect benefit: disease resistance can improve plant health to the point of potentially improving some yield components, at least in disease-prone scenarios. However, when it came to thousand-grain weight (TGW), a few transgenic lines showed a small decrease relative to the control. For example, the chitinase line had a TGW about 2% lower than the control, and the AMP line had about a 1% lower TGW. These differences were statistically significant (P < 0.05) but very small in magnitude. A 1%-2% reduction in grain weight is quite minor and would have negligible impact on overall yield, especially if compensated by a few more grains per ear or per plant. The reason behind this slight decrease in grain weight isn’t fully clear. The researchers speculated it might have to do with the expression of the transgenes in the grains affecting grain composition very slightly - maybe the accumulation of a foreign protein in the grain marginally changes how resources are allocated to starch vs. protein, etc. There is some precedence: other studies have noted that when you alter grain composition (like suppressing a storage protein or adding a new protein), sometimes grain size or weight can shift slightly. For instance, they mention that transgenic barley with reduced levels of certain storage proteins saw a small drop in TGW but an increase in grain number per ear, which echoes what they’re seeing: a tiny reduction in individual grain weight might be balanced by more grains. Importantly, total grain yield per plant (or per area) was not significantly different between transgenic lines and the control. They calculated grain yield and found that, for example, the chitinase line’s average grain yield per plant was about 2.5% higher than the control’s, the AMP line was about the same as control, and the dual-gene line was about 3.0% higher than control. None of these differences were statistically significant - they’re within the normal variation range. Essentially, the transgenic barley yielded the same as the normal barley under the test conditions (which in this case were mostly disease-free or controlled conditions).
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